Strings interview questions

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

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.

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

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.

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.

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

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

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

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.

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

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.

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

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