Interview questions

Find All Possible Recipes from Given Supplies

Given recipes whose ingredients may include other recipes and an initial set of supplies, determine which recipes can be produced; the core challenge is dependency…

Companies: Amazon, Google, Tesla

Array · Directed Acyclic Graph · Graph Theory · Hash Table

Last reported Feb 2026

Find All Anagrams in a String

Given strings s and p, return all start indices of substrings in s that are anagrams of p; the core challenge is to detect equal…

Companies: Amazon, Databricks, Microsoft

Hash Table · Sliding Window · String

Last reported Feb 2026

Maximum Nesting Depth of the Parentheses

Given a valid parentheses string, compute its maximum nesting depth — the largest number of parentheses that are open at the same time. (Equivalent to…

Companies: Meta, Rippling

Bracket Sequences · Stack · String

Last reported Feb 2026

Find the Closest Palindrome

Given a numeric string n (up to 18 digits), find the closest integer palindrome different from n (ties broken by smaller value). The typical approach…

Companies: Meta, Uber

Math · String

Last reported Jan 2026

String Compression

Compress an array of characters in-place by replacing each run of consecutive identical characters with the character followed by its run length (omit the length…

Companies: Apple, Goldman Sachs, Morgan Stanley, Pinterest +1

String · Two Pointers

Last reported Jan 2026

Expression Add Operators

Given a digit string and a target value, insert the binary operators +, -, and * between digits (without creating operands with leading zeros) to…

Companies: LinkedIn, Meta, Pinterest

Backtracking · Math · String

Last reported Jan 2026

Shortest Word Distance

Given a list of words and two distinct target words, find the minimum absolute index distance between any occurrence of the two targets. This is…

Companies: LinkedIn, Snowflake

Array · String

Last reported Dec 2025

Minimum Add to Make Parentheses Valid

Given a string of '(' and ')', return the minimum number of parentheses insertions needed to make the string valid. This is solved greedily by…

Companies: Meta, Microsoft

Bracket Sequences · Greedy · Stack · String

Last reported Dec 2025

Longest Repeating Character Replacement

Find the length of the longest substring that can be turned into all the same letter by performing at most k character replacements; this is…

Companies: D. E. Shaw, Goldman Sachs, Meta, Microsoft +1

Hash Table · Sliding Window · String

Last reported Oct 2025

Multiply Strings

Multiply two non-negative integer strings without converting them to numeric types or using BigInteger: compute the product by simulating grade-school digit-by-digit…

Companies: Meta, Microsoft, Pinterest

Math · Simulation · String

Last reported Sep 2025

Remove Invalid Parentheses

Given a string containing letters and parentheses, remove the minimum number of parentheses to produce all distinct valid parentheses strings and return them. The core…

Companies: Meta

Backtracking · Breadth-First Search · String

Last reported May 2025

Restore IP Addresses

Partition the digit string into exactly four segments (by inserting three dots) so each segment is between 0 and 255 and has no leading zeros…

Companies: Microsoft, Motive, NVIDIA

Backtracking · String

Last reported Apr 2025

Minimum Insertions to Balance a Parentheses String

Given a string of '(' and ')', return the minimum number of insertions needed to make it balanced under the rule that each '(' must…

Companies: Bloomberg, Meta

Bracket Sequences · Greedy · Stack · String

Last reported Mar 2025

Reorganize String

Rearrange the characters of a string so that no two adjacent characters are the same, returning any valid permutation or "" if none exists. Key…

Companies: Amazon, D. E. Shaw, Tesla

Counting · Greedy · Hash Table · Heap (Priority Queue)

Last reported Jan 2025

Smallest String With Swaps

Given a string and allowed index swap pairs, view pairs as edges in a graph to find connected components where characters can be freely permuted…

Companies: Goldman Sachs, Google

Array · Breadth-First Search · Depth-First Search · Hash Table

Last reported Oct 2024

Add Binary

Add two binary strings and return their sum as a binary string by performing digit-wise addition from the least significant bit with carry, handling unequal…

Companies: Meta

Bit Manipulation · Math · Simulation · String

Alphabet Board Path

Convert each target letter to its board coordinates and output a shortest sequence of moves (U/D/L/R) plus '!' to spell the string by walking between…

Companies: Atlassian

Hash Table · String

Brace Expansion

Given a string with brace-enclosed comma-separated option groups and implicit concatenation (e.g., "{a,b}c{d,e}"), generate all unique strings formed by choosing one option…

Companies: Anduril

Backtracking · Breadth-First Search · Sorting · Stack

Count Binary Substrings

Count the non-empty substrings of a binary string that contain an equal number of 0s and 1s with all 0s and all 1s each grouped…

Companies: D. E. Shaw

String · Two Pointers

Count Vowel Substrings of a String

Count the number of contiguous substrings that consist only of vowels and contain all five vowels (a, e, i, o, u) at least once. The…

Companies: D. E. Shaw, Expedia, Salesforce, Snowflake

Hash Table · String

Distinct Subsequences

Count the number of distinct subsequences of s that equal t — i.e., the number of ways to delete characters from s (keeping relative order)…

Companies: Swiggy

Dynamic Programming · String

Encrypt and Decrypt Strings

Implement an Encrypter that maps each character to a two-letter code and supports encrypting by replacing characters and decrypting by counting how many dictionary words…

Companies: Duolingo

Array · Design · Hash Table · String