Questions

Implement findLast and findLastIndex — scan an array from the end for the last element matching a predicate.

Implement Array.prototype.myAt — return the element at a given index, supporting negative offsets from the end.

Implement Array.prototype.every — return false as soon as an element fails the predicate, true when empty.

Implement Array.prototype.filter from scratch as a method on the array prototype.

Implement Array.prototype.flat — flatten nested arrays to a given depth (default 1, Infinity for all levels), dropping holes.

Implement Array.prototype.forEach — run a callback on each element as (value, index, array), skipping sparse holes.

Implement Array.prototype.includes — test membership with SameValueZero so NaN matches, honoring negative fromIndex.

Implement Array.prototype.indexOf — first index of a value by strict equality, supporting a negative fromIndex.

Implement Array.prototype.some — return true as soon as any element passes the predicate, false when empty.

Implement a custom Array.prototype.square method that returns a new array with each value squared.

Implement a function that splits an array into groups of a given size, with the last group holding the remainder.

Implement a function that constrains a number to lie within an inclusive minimum and maximum range.

Implement a function that returns a new array with every falsy value stripped out.

Implement a function that consolidates rows sharing the same user into a single grouped record.

Implement a function that returns the elements from the first array that do not appear in the second.

Implement a function that drops trailing array elements as long as a predicate keeps returning truthy.

Implement a function that drops leading array elements as long as a predicate keeps returning truthy.

Implement a function that replaces array elements with a given value between an optional start and end index.

Implement a function that checks whether an array contains any duplicate numbers.

Implement a function that returns the index of the first array element matching a predicate, or -1 if none match.

Implement a function that returns the index of the last array element matching a predicate, or -1 if none match.

Implement a function that returns the single missing number from a sorted sequence of integers.

Find the first failing version among 1..n where a monotonic isBad check flips from false to true — a boundary binary search using the fewest checks.

Implement a function that builds an object from an array of [key, value] pair tuples.

Implement a function that checks whether a number lies within a half-open range, swapping bounds when needed.

Implement a function that returns the unique values present in every input array.

Implement lodash keyBy — index a collection into an object keyed by an iteratee's return, keeping the last item for each key.

Implement a function that joins an array of strings into a grammatical list with commas and a conjunction.

Implement Map.groupBy — group an iterable into a Map whose keys can be any value, preserving key insertion order.

Implement a function that returns the array element producing the largest value when run through an iteratee.

Implement a function that computes the arithmetic mean of the numbers in an array.

Implement a function that returns the array element producing the smallest value when run through an iteratee.

Implement nth — return the element at index n, counting from the end when n is negative, so head is nth(0) and last is nth(-1).

Implement a function that computes the maximum profit obtainable from one buy and one sell of a stock.

Implement a function that finds two numbers in an array that add up to a given target.

Implement a function that builds an array of numbers from start up to end, stepping by a given increment.

Implement a function that builds an array of numbers from end down to start in descending order.

Implement String.prototype.repeat — join a string n times, throwing RangeError on a negative or infinite count.

Implement lodash sumBy and meanBy — total and average an array by an iteratee that maps each element to a number.

Implement take and takeWhile — grab the leading n elements, or the leading run that satisfies a predicate.

Implement a function that wraps occurrences of a search term within a string in highlight markup.

Implement times — invoke a function n times and collect the results into an array.

Implement a function that returns a new array with duplicate values removed while preserving original order.

Implement without — return a copy of an array with the given values excluded, matched by SameValueZero.

Implement lodash xor — return the values that appear in exactly one of the given arrays, with duplicates removed.

Move all zeroes to the end of an array in place while keeping the non-zero elements in their original order.

Implement a setInterval wrapper that returns a function which stops the interval when invoked.

Implement a setTimeout wrapper that returns a function you can call to cancel the pending callback.

Implement a function that composes functions right-to-left so the output of each feeds into the next.

Implement a function that, given several values, returns a function that yields each one in turn and loops forever.

Implement a function that delays invoking another function until a specified period of inactivity has passed.

Implement a factory that takes a starting integer and returns a function that returns the next value on each call.

Implement a function that returns the count of arguments passed to it at call time.

Implement a function that wraps a callback so it runs at most one time and reuses that result thereafter.

Run async tasks in sequence, feeding each result into the next, stopping the chain on the first rejection.

Implement a function that returns a promise resolving after the specified number of milliseconds.

Implement a cache whose entries expire a fixed time after their last access, not after being set.

Buffer bursty streamed text and emit it one character at a time at a steady cadence, with flush and stop controls.

Implement a function that limits how often a wrapped function can be invoked within a time window.

Implement Array.prototype.myReduce — the reduce method from scratch, including the empty-array + initial-value edge cases.

Build an analytics client that queues tracked events, flushes them in batches, and retries failed sends with backoff.

Implement an async debounce that resolves only the newest call and discards the results of superseded ones.

Implement an async memoize that caches results by key for a TTL and coalesces concurrent calls for the same key.

Buffer events and flush them in batches when a size threshold or a max-wait timer is reached.

Implement before and after — cap how many times a function runs, or delay invoking it until the Nth call.

Implement a simplified cva that builds class names from base styles, variant tables, and default values.

Implement a wrapper that intercepts console.log calls and records their arguments for later inspection.

Implement a function that transforms a multi-argument function into a chain of single-argument calls.

Implement a flexible curry where each call can supply any number of arguments until the original arity is reached.

Extend debounce with cancel and flush methods to abort or immediately invoke pending calls.

Extend debounce with a maxWait option that forces a call after a maximum delay even under constant activity.

Build a DI container that resolves a service dependency graph, caches singletons, and detects circular dependencies.

Implement a function that counts the number of unique paths a robot can take from the top-left to bottom-right of an m by n grid.

Implement flow — compose functions left to right so each output feeds the next.

Implement Function.prototype.myBind — return a new function with a fixed `this` and optional preset arguments.

Build an axios-style client whose request and response interceptors transform each call as it passes through the chain.

Implement a function that wraps a callback so it runs at most N times and returns the last result thereafter.

Implement a factory that returns a counter object with methods to read, increment, decrement, and reset its value.

Implement a function that caches results of a single-argument function so repeat calls return instantly.

Implement a memoize helper that caches results for functions called with any number and type of arguments.

Extend memoize with a custom key resolver and cache controls (.clear() and .delete(key)).

Build atom-based state with primitive and derived atoms that recompute and notify subscribers on change.

Build a Redux core with createStore, combineReducers, and applyMiddleware over a subscribe/dispatch loop.

Implement negate, overEvery, and overSome — build new predicates by combining existing ones.

Implement partial and partialRight — pre-fill some of a function's arguments, with placeholder support.

Implement a function that combines the results of two promises into a single value using a merger function.

Implement a function that races a promise against a timer and rejects if the promise doesn't settle in time.

Implement a function that wraps a Node-style error-first callback function so it returns a promise.

Extend promisify so the wrapped function can override the resolved value via a custom override hook.

Implement a sliding-window rate limiter that decides which task timestamps fit within the allowed quota.

Implement the curried Redux middleware chain with working thunk and logger middleware.

Build memoized selectors that recompute only when their input selections change by reference.

Wrap an async call with retries, backoff, and a per-attempt timeout so transient failures recover.

Implement an interval helper that exposes start, pause, and resume controls while preserving elapsed progress.

Implement a small schema library that validates primitives and flat object shapes with composable rules.

Build a tiny schema validation library that supports chainable min and max rules on primitive types.

Implement a function that decides whether a string can be broken into a sequence of words from a given dictionary.

Build reactive signals with automatic dependency tracking so computed values and effects update on change.

Implement a Singleton class that always hands back the same instance no matter how many times you construct it.

Return cached data instantly, serving stale values while revalidating them in the background.

Implement a curried sum function that accepts numbers one call at a time and returns the running total when invoked with none.

Build a small test runner that supports nested describe suites and reports tests with their full spec names.

Extend a tiny test runner with beforeEach and afterEach hooks that are inherited from outer suites.

Extend throttle with cancel and flush methods plus leading and trailing edge options.

Build a schema-driven form validator with composable per-field rules, cross-field checks, and async validators that report all errors.

Extend curry with placeholder support, so arguments can be supplied in any position across calls.

Run a queue of tasks in time slices, yielding control between them so the main thread stays responsive.

Implement a curry helper that turns a variadic function into one that can be called repeatedly with any number of arguments.

Build an in-memory query builder inspired by Drizzle with table helpers, filters, sorting, and pagination.

Extend an in-memory query builder inspired by Drizzle with select projections and column aliases.

Implement an async map that processes an array with a bounded number of in-flight tasks.

Implement an async middleware composer that chains functions Koa-style, threading a shared context through next.

Return an array where each entry is the product of every element except the one at that index, without division and in O(n).

Implement Array.prototype.myConcat — merge arrays and values into a new array, spreading nested arrays one level deep.

Implement Array.prototype.find and findLast — return the first or last element matching a predicate, or undefined.

Implement Array.prototype.flatMap — map each element, then flatten the mapped results by one level.

Implement Array.prototype.myMap — return a new array with the callback applied to each element, skipping holes.

Implement Array.prototype.myReduce — fold an array down to one value, handling sparse arrays and missing initial values.

Implement Array.prototype.reduceRight — fold an array right-to-left, throwing on an empty array with no initial value.

Implement Array.prototype.splice — remove and insert elements in place, returning the removed ones, with clamped indices.

Implement a utility that conditionally joins class name arguments into a single space-separated string.

Implement a function that tallies how many array elements map to each key produced by an iteratee.

Recursively freeze an object and every nested object and array, making the whole structure deeply immutable.

Implement a function that locates a target integer in a sorted array that has been rotated at an unknown pivot.

Implement a function that recursively flattens a nested array into a single-level array.

Implement Function.prototype.myApply — invoke the function with a given `this` and an array of arguments.

Implement a function that buckets array elements into an object keyed by the value an iteratee returns for each.

Implement a function that intersects arrays by comparing values produced by an iteratee, keeping uniqueness.

Implement a function that intersects arrays using a user-supplied comparator to decide equality between elements.

Rotate an n×n matrix 90 degrees clockwise and return the result as a new array.

Implement a function that finds the contiguous subarray with the largest product, handling negatives and zeros.

Implement a function that finds the contiguous subarray with the largest sum.

Implement a function that finds the maximum amount of water that can be trapped between two walls.

Implement orderBy — stably sort objects by multiple keys, each ascending or descending.

Implement partition — split an array into elements that pass a predicate and those that fail, in one pass.

Decide whether an array can split into two subsets with equal sums — a subset-sum dynamic-programming problem over half the total.

Find the k-th smallest element of an unsorted array in average linear time by partitioning, without fully sorting it.

Implement a function that finds the minimum value in a sorted array that has been rotated at an unknown pivot.

Implement a function that returns unique values across input arrays using a custom iteratee to determine identity.

Implement zip, unzip, and zipObject — interleave arrays into tuples and back, padding ragged lengths.

Implement the ES2023 change-by-copy trio — toSorted, toReversed, and with — that copy an array instead of mutating it.

Implement lodash pull and pullAll — remove every occurrence of the given values from an array in place, mutating the original.

Implement lodash shuffle and sampleSize with an unbiased Fisher-Yates swap, taking an injectable RNG so shuffles are testable.

Extend the classNames utility to dedupe class names and resolve function arguments lazily.

Implement a function that filters an array of row objects by a flexible field-and-condition specification.

Find the median of two sorted arrays in logarithmic time by binary-searching for the partition that splits all the elements into equal halves.

Implement a function that returns the number of declared parameters of a given function.

Implement a function that returns a new object with every value transformed by a mapper callback.

Implement Object.entries — return an object's own enumerable string-keyed [key, value] pairs in insertion order.

Implement Object.fromEntries — build an object from any iterable of [key, value] pairs, with later keys winning.

Implement a function that returns the element count of any collection — array, string, object, Map, or Set.

Implement a set of helper functions that report the primitive type of any JavaScript value.

Implement a function that decides whether a value is empty across arrays, strings, objects, Maps, Sets, and primitives.

Implement a function that returns a new object with every key converted to camelCase, recursing into nested objects.

Implement a function that returns a deep copy of an object with all falsy values stripped from nested structures.

Implement a function that checks whether an object satisfies a source schema of predicate validators.

Implement a function that recursively clones a JSON-serializable value without sharing references.

Implement a function that recursively merges two objects, combining nested properties rather than overwriting them.

Implement a function that returns a copy of a value with the given keys stripped from every nested object.

Implement an EventEmitter class supporting on, off, and emit to register and trigger listeners.

Implement an event emitter where subscribe returns a handle whose release method removes that listener.

Implement Function.prototype.myCall — invoke the function with a given `this` and a list of arguments.

Implement a function that safely reads a nested object path and returns a default when any segment is missing.

Implement get and set — read and write a nested value by a path like 'a.b[0].c', creating missing containers on set.

Implement invert and invertBy — swap an object's keys and values, grouping collisions with invertBy.

Implement a function that converts a JavaScript value into its JSON string representation.

Implement a localStorage wrapper that stores values with a TTL and returns null once an entry has expired.

Implement mapKeys and mapValues — transform an object's keys or values while preserving its structure.

Build a simplified in-memory ORM with model delegates that expose basic CRUD operations.

Implement Object.assign — copy own enumerable string and symbol properties from sources onto a target, skipping nullish.

Implement pick, omit, pickBy, and omitBy — build a subset of an object by a key list or by a predicate.

Implement a function that flattens a nested object into a single-level object using dot-delimited keys.

Build a Turtle class that tracks position and heading as you issue movement and turn commands on a 2D plane.

Implement helpers that accurately identify non-primitive JavaScript values such as arrays, plain objects, dates, and maps.

Implement a function that rebuilds a nested object from a flat map of dot-delimited keys.

Wire up classical inheritance the pre-class way — link prototypes with Object.create, restore the constructor, and call the superclass constructor.

Implement newOperator — reproduce the four steps the new keyword performs, honoring the object-return override.

Implement an instanceof check — walk the prototype chain to see whether a constructor's prototype appears in it.

Implement Object.create — make a new object with a given prototype and optional property descriptors.

Implement a Backbone-style Model class that stores attributes and emits change events per key.

Implement a deep clone that copies nested values and correctly handles circular references using a visited map.

Implement a function that determines whether two values are structurally equal across nested objects and arrays.

Build a simplified in-memory ORM with field selection and eagerly included related records.

Implement structuredClone — deep-clone a value including Map, Set, Date, RegExp, typed arrays, and circular references.

Implement a function that patches shallow style objects over a text range without clobbering unrelated keys.

Implement a function that checks whether a string of brackets is properly opened and closed in order.

Convert a Roman numeral string to its integer value, handling subtractive pairs like IV and IX.

Implement String.prototype.padStart — pad a string to a target length on the left, truncating a multi-char pad.

Implement String.prototype.trim — strip leading and trailing whitespace, including Unicode whitespace, from a string.

Convert a number's string representation between any two bases from 2 to 36 — parse the digits in the source base, then re-emit them in the target base.

Add and multiply arbitrarily large non-negative integers given as decimal strings, using digit-by-digit schoolbook arithmetic with carries.

Shift each letter by a fixed amount with wraparound, preserving case and passing non-letters through — with ROT13 as the self-inverse case.

Implement a function that counts how many ways a digit string can be decoded into letters using a 1 to 26 mapping.

Compute the minimum number of insertions, deletions, and replacements to turn one string into another — the Levenshtein distance via a 2D dynamic-programming table.

Convert between Excel column titles and numbers in both directions — A is 1, Z is 26, AA is 27 — the classic bijective base-26 system with no zero digit.

Generate every well-formed combination of n pairs of parentheses by backtracking — add an open bracket while any remain, and a close bracket only while it stays balanced.

Build a translation engine with nested key lookup, variable interpolation, pluralization, and locale fallback.

Parse and format ICU MessageFormat strings with plural, select, and nested argument substitution.

Validate IPv4 dotted-quad and IPv6 addresses, handling octet ranges, leading zeros, and :: zero-group compression.

Implement a function that finds the longest substring made of one repeated character allowing up to k swaps.

Split a string every possible way so that each piece is a palindrome — backtrack over cut positions, extending a piece only while it reads the same both ways.

List every letter string a phone number could spell, mapping each digit to its keypad letters and backtracking through the choices.

Convert between Roman numerals and integers in both directions, handling subtractive notation like IV, IX, and XL.

Round, floor, and ceil a number to N decimal places without the classic floating-point drift — 1.005 must round to 1.01, not 1.00.

Implement run-length encoding: compress runs of repeated characters into count+char pairs, and decode them back.

Parse and compare two semantic version strings — major, minor, patch, and prerelease — returning -1, 0, or 1 with correct prerelease precedence.

Turn a string into a URL-safe slug: lowercase, strip accents, and collapse non-alphanumeric runs into single hyphens.

Implement a spreadsheet class that resolves numeric cell values and evaluates simple addition formulas.

Build a spreadsheet class that evaluates left-to-right arithmetic formulas referencing other cells.

Decode a Server-Sent Events stream arriving in arbitrary chunks into discrete parsed events.

Reimplement JavaScript's parseInt — skip leading whitespace, read an optional sign and radix prefix, consume valid digits for the base, and stop at the first invalid character.

Implement a template renderer that substitutes Mustache-style placeholders with values from a data object.

Implement a function that wraps every occurrence of any term from a list inside highlight markup.

Group a number's integer digits with separators — 1234567 to 1,234,567 — handling decimals, negatives, and a custom separator.

Track streaming LLM tool calls by id, accumulating argument deltas and guarding each pending, running, and done transition.

Implement a Trie data structure supporting insert, exact word search, and prefix lookup operations.

Implement lodash truncate — cut a string to a maximum length, append an ellipsis, and optionally break on the last word boundary before the limit.

Implement a URLSearchParams-style class with get, getAll, append, set, and toString over an encoded query string.

Tokenize and evaluate a math expression string with operator precedence, parentheses, and unary minus.

Convert any string between camelCase, snake_case, kebab-case, and PascalCase by tokenizing it into words first.

Implement lodash-style set and unset: write or delete a value at a deep object path, creating containers as needed.

Implement replaceAll and matchAll — replace every occurrence of a substring or global pattern, and iterate every match with its capture groups.

Spell out a non-negative integer in English words — break it into groups of three digits and name each group with its scale word.

Implement JSON.parse — a recursive-descent parser that turns a JSON string into the corresponding JavaScript value.

Parse a truncated JSON string into the best-valid value so far by completing open strings and containers.

Render markdown-so-far to HTML, holding and closing unclosed bold, inline code, and fenced code blocks.

Implement serialize and deserialize helpers that round-trip values like Date, Map, Set, and BigInt through JSON.

Decide whether a string matches a pattern containing `?` (any single character) and `*` (any sequence) — a two-dimensional dynamic-programming match over string and pattern.

Implement a countdown latch whose wait resolves once countDown has been called the required number of times.

Fetch successive pages with an opaque cursor, accumulating items and tracking whether more remain.

Implement Promise.race so it settles with the outcome of whichever input promise settles first.

Implement a function that returns a Promise already rejected with the given reason.

Fetch with a timeout that aborts the request via AbortController and honors an external abort signal.

Implement an async mutex whose acquire returns a release function, serializing access so only one holder runs at a time.

Implement an async semaphore that admits up to N concurrent holders and queues the rest until a permit frees.

Implement a task queue that runs async jobs under a concurrency limit and resolves an idle promise when drained.

Wrap a promise so it can be cancelled — the wrapper rejects on cancel and ignores the underlying settlement.

Implement a circuit breaker that trips open after repeated failures, rejects fast while open, then probes half-open.

Cache responses by URL and revalidate with an ETag, reusing cached data on a 304 Not Modified.

Implement a function that applies an async mapper to every item in an array and resolves with the results.

Coalesce all schedule calls made in one synchronous frame into a single flush on the next microtask.

Implement pollUntil — call an async function on an interval until a predicate passes or a timeout elapses.

Implement a promise pool that runs task factories with a concurrency cap and resolves to their results in order.

Implement Promise.all so it resolves with an array of results or rejects on the first rejection.

Implement Promise.allSettled from scratch, resolving to an array of fulfilled or rejected outcomes for each input.

Implement Promise.any so it resolves with the first fulfilled value or rejects with an AggregateError.

Implement Promise.resolve — wrap a value in a fulfilled promise, returning thenables unchanged and adopting their state.

Implement Promise.withResolvers — return a new promise alongside its external resolve and reject functions.

Implement retry — re-run a failing async function with a delay that grows exponentially between attempts.

Implement singleflight so concurrent calls for the same key share one in-flight promise instead of duplicating work.

Implement a minimal test runner that registers cases, runs each one, and reports pass and fail counts.

Implement Array.fromAsync: build a promise of an array from a sync or async iterable, awaiting each value in order.

Run async tasks in dependency order, executing independent ones in parallel and catching cycles.

Dedupe by idempotency key: run a task at most once per key, cache the result with a TTL, and retry on failure.

Build a long-polling loop that re-issues a held request as each returns, advances a cursor, backs off on error, and stops cleanly.

Queue writes while offline and flush them in FIFO order when the network returns, retrying failures without dropping or reordering.

Schedule async requests under a concurrency limit, always running the highest-priority waiter next with a stable FIFO tiebreak.

Wrap a WebSocket so it auto-reconnects with exponential backoff, queues sends while down, and re-emits its events.

Implement Node-style async runners — run error-first tasks in parallel or in series and collect their results.

Implement a read-write lock that allows many concurrent readers or one exclusive writer without starving writers.

Batch and cache load(key) calls made in one tick into a single batch function call, preserving order.

Build a framework-agnostic query cache with request dedup, staleTime, subscribers, and invalidation.

Implement a minimal Observable with subscribe/unsubscribe and of/from plus map and filter operators.

Apply optimistic updates immediately and roll them back on failure, even with concurrent mutations.

Extend a tiny test runner so it correctly awaits asynchronous specs and asynchronous setup or cleanup hooks.

Build a redux-saga-style interpreter that runs a generator of declarative effects and resumes it with each result.

Build a mini reactive-streams library: a cold Observable and pipeable operators composed with a .pipe() chain.

Implement a function that counts the distinct ways to climb to the top of a staircase taking one or two steps.

Maximize the value packed into a weight-limited knapsack when each item can be taken at most once — the classic 0/1 dynamic-programming table.

Implement a function that returns every unique combination of reusable candidates that sums to a target.

Implement a function that counts the number of distinct islands of connected cells in a 2D binary grid.

Implement a function that walks an arbitrarily nested structure and applies a transform to every leaf value.

Implement depth-first traversal of a directed graph, exploring each branch fully before backtracking.

Raise a base to an integer exponent in logarithmic time using exponentiation by squaring, handling negative exponents.

Compute the greatest common divisor with Euclid's algorithm and the least common multiple, for two numbers or a whole list.

Implement a function that serializes a tree-shaped object into a pretty-printed HTML string with indentation.

Implement merge sort recursively by splitting the array and merging the sorted halves back together.

Generate every permutation and every subset of an array with the same backtracking template — choose, recurse, and undo.

Implement quick sort recursively, partitioning around a pivot and sorting each side independently.

Implement JSON.stringify with full spec support including replacer, indentation, and circular reference detection.

Place N queens on an N×N board so none attack another — a classic backtracking search that places one queen per row and prunes column and diagonal conflicts.

Extend a tiny schema validator to handle nested object and array shapes plus optional fields.

Fill a 9×9 Sudoku grid by backtracking — try each digit in the next empty cell, checking its row, column, and 3×3 box, and undo on a dead end.

Build serialize and deserialize that preserve referential identity — shared references and circular structures round-trip intact.

Implement a function that returns whether two binary trees have identical structure and node values.

Implement a function that returns the maximum depth from root to leaf in a binary tree.

Implement a function that merges two sorted linked lists into a single sorted linked list.

Implement a function that mirrors a binary tree by swapping the left and right children of every node.

Implement a function that reverses a singly linked list in place and returns the new head.

Build a queue data structure supporting enqueue, dequeue, peek, and size in FIFO order.

Build a stack data structure that supports the standard push, pop, peek, and size operations.

Implement a function that determines whether two strings are anagrams of each other.

Assign users to weighted experiment variants deterministically, with a traffic gate and independent buckets per experiment.

Implement a function that returns the kth smallest value in a binary search tree.

Implement a function that finds the lowest common ancestor of two nodes in a binary search tree.

Build a binary tree data structure with the essential insert, traverse, and search operations.

Implement a function that returns the values of a binary tree grouped by level from top to bottom.

Implement a function that reconstructs a binary tree given its preorder and inorder traversal sequences.

Implement a function that determines whether one binary tree appears as a subtree of another.

Build a Bloom filter — a compact probabilistic set that answers membership with no false negatives but possible false positives, using a bit array and several hash functions.

Implement breadth-first traversal of a directed graph, visiting nodes level by level from a start vertex.

Implement a function that decides whether a set of courses can be finished given their prerequisite pairs.

Implement a function that removes the nth-from-end node from a singly linked list in one pass.

Build a double-ended queue with constant-time push and pop at both the front and the back, backed by a doubly linked list.

Evaluate feature flags with targeting rules and a deterministic percentage rollout that stays sticky per user.

Build increment and decrement counters that merge by per-node maxima into a conflict-free convergent total.

Implement a function that produces a deep copy of a connected, undirected graph given a reference node.

Implement a function that counts the number of connected components in an undirected graph given its edges.

Implement a function that determines whether a given undirected graph forms a valid tree.

Build a singly linked list data structure with the standard insert, remove, and traversal operations.

Implement a function that detects whether a singly linked list contains a cycle.

Implement a function that returns the length of the longest run of consecutive integers found in an unsorted array.

Implement a function that returns the length of the longest substring containing no duplicate characters.

Build a last-write-wins map whose entries merge by timestamp with a deterministic node-id tiebreak.

Implement a class that records timestamped writes and returns the most recent value at or before a queried timestamp.

Implement a function that zeroes out every row and column in a matrix that originally contained a zero, ideally in place.

Extend a simplified in-memory ORM with richer filtering predicates and multi-field sorting.

Implement a function that returns the k most frequent integers in an array, breaking ties consistently.

Store entities flat by id, normalizing nested relations and merging updates immutably.

Build an observed-remove set where a concurrent add and remove converge with the add winning.

Build a FIFO queue out of two LIFO stacks — pour one stack into the other so the reversed order dequeues oldest-first in amortized constant time.

Implement a function that reorders a singly linked list by interleaving nodes from the front and the reversed back half.

Implement a function that groups an array of strings so anagrams of each other end up in the same bucket.

Implement a function that overwrites the style on a given text range and normalizes the resulting range list.

Implement a function that schedules tasks with a cooldown between identical ones and returns the minimum total time.

Implement a class that tracks value history and exposes undo and redo navigation across the timeline.

Build a user database class that supports CRUD operations plus undo and redo across the operation history.

Build a disjoint-set structure with near-constant-time union and find, using path compression and union by rank to keep the trees flat.

Implement a function that determines whether a binary tree satisfies the binary search tree ordering invariant.

Implement a data structure that supports adding words and searching with a wildcard character that matches any letter.

Build lazy, chainable iterator helpers — map, filter, take, drop, and flatMap — that pull one value at a time.

Build a binary search tree with insert, search, and delete operations preserving the BST invariant.

Implement a function that returns the maximum sum of node values along any path in a binary tree.

Implement functions that convert a binary tree to a string and reconstruct the same tree back from that string.

Implement Dijkstra's algorithm to compute shortest paths from a source vertex in a weighted graph.

Extend an in-memory query builder inspired by Drizzle with innerJoin and leftJoin between related tables.

Build a Fenwick tree for logarithmic prefix-sum queries and point updates, using the lowest-set-bit trick to walk responsibility ranges.

Implement a function that returns every word from a dictionary that can be traced through adjacent cells in a grid.

Implement a binary heap data structure supporting push, pop, peek, and heapify with the standard ordering invariant.

Implement heap sort by building a max-heap and repeatedly extracting the largest element.

Implement produce so mutating a draft proxy yields a new immutable state with structural sharing.

Merge k pre-sorted singly-linked lists into one sorted list in O(n log k) time.

Implement a data structure that ingests integers one at a time and reports the running median in logarithmic time.

Build an immutable list where every update returns a new version that shares unchanged nodes with the old one — structural sharing over a cons list.

Build a segment tree over an array for logarithmic range-sum queries and point updates, each tree node holding the aggregate of its slice.

Build a replicated growable array for text whose positional-id inserts and deletes converge across replicas.

Build a skip list — a sorted set layered with express lanes of linked lists so search, insert, and delete run in expected logarithmic time.

Build a spreadsheet that recomputes dependent cells when inputs change and detects circular references.

Implement a slice operation over text annotated with overlapping style ranges, preserving alignment.

Implement a function that replaces a text range and keeps the surrounding style ranges normalized.

Build a class that tracks draft values and commits them as batch checkpoints for undo and redo navigation.

Build a user database that buffers draft mutations and commits them as batch undo and redo checkpoints.

Implement bubble sort, repeatedly swapping adjacent out-of-order pairs until the array is sorted.

Implement insertion sort by building the sorted portion one element at a time from the input.

Implement a function that determines whether a person can attend every meeting given their time intervals.

Implement selection sort to order an array by repeatedly picking the smallest remaining element.

Implement binary search on a sorted array, returning the index of the target or -1 when absent.

Sort integers without comparisons — counting sort tallies occurrences into buckets, and radix sort applies it digit by digit from the least significant.

Implement a function that returns the minimum number of intervals to remove so the remaining ones do not overlap.

Implement a function that inserts a new interval into a sorted list and merges any resulting overlaps.

Implement a function that merges all overlapping intervals in a list and returns the consolidated set in sorted order.

Implement a function that returns the fewest meeting rooms required to host a list of time intervals without conflicts.

Implement a function that sorts positioned canvas elements into natural left-to-right, top-to-bottom reading order.

Implement a function that groups misaligned 2D canvas elements into rows, then sorts them into a natural reading order.

Implement a function that returns every unique triplet of distinct indices whose values sum to zero.

Pick items at random in proportion to their weights using prefix sums and a binary search, with an injectable RNG so picks are testable.

Implement a function that returns a topological ordering of nodes in a directed acyclic graph.

Implement a function that reverses the order of the bits in the binary representation of a number.

Implement a function that counts the number of 1 bits in the binary representation of an integer.

Implement Object.is — same-value equality that treats NaN as equal to itself and keeps +0 distinct from -0.

Implement a function that returns whether a string reads the same forwards and backwards.

Implement a function that returns an array of set-bit counts for every integer from 0 up to n.

Implement a function that decides whether you can reach the last index of an array using each element as a max jump.

Implement a function that returns the longest palindromic substring contained within a given string.

Implement a function that checks whether a target word can be traced through adjacent cells in a 2D character grid.

Compute the integer square root — the floor of the real square root — using Newton's method, without Math.sqrt.

Implement a function that returns the length of the longest subsequence common to two input strings.

Implement a function that returns the length of the longest strictly increasing subsequence in an array.

Implement a function that walks a 2D matrix in clockwise spiral order and returns the visited values.

Find the area of the largest all-ones square in a binary matrix, where each cell's square size is one more than the smallest of its top, left, and top-left neighbors.

Implement a function that returns the fewest coins needed to make a target amount, or -1 when no combination works.

Find the cheapest path from the top-left to the bottom-right of a grid, moving only right or down, by summing each cell with the smaller of the two ways to reach it.

Implement a function that computes the maximum money you can rob from a row of houses without picking two adjacent ones.

Implement a function that maximizes loot from houses arranged in a circle without robbing two adjacent ones.

Implement a function that returns every grid cell from which water can flow to both the Pacific and Atlantic oceans.

Implement a function that counts every palindromic substring within a string, including overlapping occurrences.

Test whether a number is prime and generate all primes up to n with the Sieve of Eratosthenes.

Search a matrix whose rows and columns are both sorted by walking a staircase from the top-right corner, eliminating a whole row or column at each step.

Build a pure, immutable reducer that opens an assistant message, appends streamed deltas, and finalizes it.

Implement a function that adds two integers using only bitwise operators, without using + or -.

Order distributed events with vector clocks, detecting whether two events are causal or concurrent.

Implement base64 encoding and decoding from scratch — pack bytes into 6-bit groups, map to the alphabet, and handle padding.

Run many logical channels over one WebSocket — route each incoming frame to the right channel and clean up on leave.

Resume a dropped connection without gaps — track sequence numbers, request a replay from the last seen, and de-duplicate redelivered messages.

Given words sorted in an unknown alphabet's order, reconstruct the alphabet.

Build MobX-style observables with autorun and computed that re-run when the data they read changes.

Transform concurrent insert and delete operations so replicas converge to the same text.

Implement a function that converts a list of styled text ranges into a canonical, properly nested HTML string.

Implement a function that returns the smallest window of a string that contains every character of another string.

Build a state-machine engine with events, guards, entry and exit actions, and context updates.

Implement get/set/remove over document.cookie, handling encoding and expiry.

Implement a deep clone of a DOM node and its subtree (element, text, and attributes) without cloneNode.

Implement a function that returns the height (max depth) of a DOM element's subtree.

Implement a delegated event listener that matches events bubbling up from descendants against a selector.

Implement a function that builds a unique CSS selector path from the root to a given element.

Implement a function returning the set of distinct tag names used in a DOM subtree, in document order.

Implement a jQuery-style helper that gets or sets inline CSS properties on a DOM element.

Implement a function that finds the element immediately to the right of a target at the same tree depth.

Implement a breadth-first traversal of a DOM tree, returning elements level by level.

Implement a function that locates the node in a mirrored DOM tree occupying the same path as a given node.

Implement Element.matches: test whether an element satisfies a compound CSS selector (tag, id, class, attribute).

Build a jQuery-style wrapper whose methods return this so calls like addClass().text() chain.

Implement a state machine from a config of states and transitions, with send, guards, and entry actions.

Serialize a form's fields into a nested object, handling checkboxes, multi-selects, and bracket names.

Implement a function that returns all DOM elements containing every one of the specified class names.

Implement a function that returns all DOM elements whose computed style matches a given property and value.

Implement a function that walks a DOM tree and returns every descendant element matching a given tag name.

Build a client-side router over location.hash with route params and a change subscription.

Build a client-side router over the History API (pushState/popstate) with path params.

Implement a simplified HTML sanitizer that strips out unsafe tags and attributes from a given DOM tree.

Implement a function that recursively compares two DOM trees and returns whether they are structurally equal.

Implement a scroll/resize-driven fallback that reports when observed elements enter the viewport.

Implement chainable addClass, removeClass, toggleClass, and hasClass helpers on a DOM element wrapper.

Resolve a dotted path with array indices and a wildcard against a nested object, returning matches.

Implement the jsx() factory (type, props, children) that a JSX transform compiles to.

Swap each image's data-src into src as it nears the viewport, using an IntersectionObserver.

Implement a fixed-capacity least-recently-used cache with O(1) get and put via a map plus a linked list.

Parse a subset of Markdown (headings, bold, italics, links, code) into an HTML string.

Implement a string template engine with {{ variable }} interpolation and nested-path lookup.

Build a mini MutationObserver that diffs a subtree on demand and reports added and removed nodes.

Implement a registry that associates values with DOM nodes without leaking memory once nodes are gone.

Build a tiny state store with getState, setState, and subscribe that notifies listeners on change.

Implement an event bus whose subscriptions support wildcard segments matching any single topic level.

Implement querySelectorAll for descendant-combinator selectors, returning matches in document order.

Build a polling-based ResizeObserver that reports elements whose content-box size has changed.

Implement an html tagged-template function that interpolates values safely into a DOM fragment.

Wire an input and a model object so edits to either side stay in sync via events and a setter.

Implement a diff that patches real DOM from an old vnode tree to a new one, minimizing changes.

Implement createElement to build a virtual DOM tree and render to turn it into real DOM nodes.

Build an emitter whose emit awaits async listeners, with once, off, and serial or parallel dispatch.

Reorder a list by pointer drag, computing the target index from the cursor over item midpoints.

Implement a function that finds all DOM elements matching an ancestor-to-descendant tag-name hierarchy.

Tokenize an HTML string and build a nested node tree, handling attributes, void, and nested tags.

Run a queue of tasks in time-sliced batches, yielding between slices to keep the frame responsive.

Reconcile two keyed child lists into a minimal set of DOM inserts, moves, and removals.

Implement a function that finds the deepest common ancestor whose hiding would conceal every target element.

Build reactive state with a Proxy that tracks reads and re-runs registered effects on write.

Implement a function that walks an HTML document's headings and builds a nested table of contents.

Implement a function that gathers the text content lying between two DOM nodes in document order.

Compute a tooltip's position around an anchor, flipping and shifting to stay inside the viewport.

Compute the visible slice and spacer offsets to render only on-screen rows of a huge list.

Implement a hook that exposes a boolean value alongside setTrue, setFalse, and toggle helpers.

Implement a hook that fires a callback whenever the user clicks anywhere in the window, cleaning up on unmount.

Implement a hook returning the last copied text and an async copy function built on the Clipboard API.

Implement a hook that exposes a numeric count along with increment, decrement, and reset helpers.

Rewrite useCounter so the returned helpers keep stable identities across renders.

Implement a hook that returns the current value of a sequence and advances to the next on demand.

Implement a hook that steps through an array with wraparound, exposing the current item and next/prev/set.

Implement a hook that falls back to a default value whenever the underlying state becomes null or undefined.

Implement a hook that sets document.title and restores the previous title when the component unmounts.