Interview questions

Trapping Rain Water

Given an array of non-negative heights representing elevation bars of width 1, compute the total units of water that can be trapped between them after…

Companies: Amazon, Bloomberg, Goldman Sachs, Google +6

Array · Dynamic Programming · Monotonic Stack · Stack

Last reported Oct 2026

Maximum Number of Points From Grid Queries

For each query threshold, compute how many distinct cells you can reach from the top-left by moving 4-directionally through cells whose value is strictly less…

Companies: Uber

Array · Breadth-First Search · Heap (Priority Queue) · Matrix

Last reported Sep 2026

3Sum

Find all unique triplets in an integer array that sum to zero, ensuring no duplicate triplets in the output. The core challenge is efficiently enumerating…

Companies: Amazon, Apple, Bloomberg, Google +5

Array · Sorting · Two Pointers

Last reported Sep 2026

Closest Binary Search Tree Value II

Given a BST, a real-valued target and an integer k, return the k node values in the tree closest to the target. The challenge is…

Companies: Amazon, LinkedIn

Binary Search Tree · Binary Tree · Depth-First Search · Heap (Priority Queue)

Last reported Sep 2026

Palindromic Substrings

Count the number of contiguous substrings of s that are palindromes. With |s| up to 1000, the core challenge is to enumerate/detect all palindromic centers…

Companies: Goldman Sachs, Meta, Microsoft

Dynamic Programming · String · Two Pointers

Last reported Sep 2026

Find Median from Data Stream

Maintain a data structure that supports adding integers from a stream and returning the current median efficiently for many interleaved addNum and findMedian calls. The…

Companies: Adobe, Amazon, D. E. Shaw, Intuit +4

Data Stream · Design · Heap (Priority Queue) · Sorting

Last reported Aug 2026

Longest Palindromic Substring

Given a string s, return the longest substring that reads the same forwards and backwards. The core challenge is efficiently finding palindromic spans around centers…

Companies: Adobe, Amazon, Bloomberg, Goldman Sachs +6

Dynamic Programming · Manacher · String · Two Pointers

Last reported Aug 2026

Shortest Way to Form String

Given a source and target string, return the minimum number of subsequences of source that need to be concatenated to form target (or -1 if…

Companies: Pinterest

Binary Search · Greedy · String · Two Pointers

Last reported Aug 2026

Squares of a Sorted Array

Given an integer array sorted in non-decreasing order (which may contain negative numbers), return a new array of the squares of each number, also sorted…

Companies: Bloomberg, Instacart, Uber

Array · Sorting · Two Pointers

Last reported Aug 2026

Rotate Array

Rotate an integer array to the right by k steps (k may exceed the array length), effectively moving each element to index (i+k) mod n…

Companies: Apple, Microsoft, Nutanix, TikTok

Array · Math · Two Pointers

Last reported Jun 2026

Valid Palindrome

Check whether a string becomes a palindrome after lowercasing and removing all non-alphanumeric characters. The typical challenge is to do this efficiently (O(n)) by scanning…

Companies: Apple, Bloomberg, Meta

String · Two Pointers

Last reported Jun 2026

Palindrome Linked List

Companies: eBay, Meta, Microsoft

Linked List · Recursion · Stack · Two Pointers

Last reported May 2026

Remove Duplicates from Sorted Array

Given a sorted array, remove duplicates in-place so each unique value appears only once (preserving order) and return the count k of unique elements. This…

Companies: Bloomberg, Google, Meta, Microsoft

Array · Two Pointers

Last reported May 2026

Happy Number

Determine whether iterating n -> sum of the squares of its digits eventually reaches 1 or falls into a repeating cycle; the core task is…

Companies: Snowflake

Floyd's Cycle Finding Algorithm · Hash Table · Math · Two Pointers

Last reported May 2026

Merge Sorted Array

Given two sorted arrays nums1 and nums2 and counts m and n (nums1 has length m+n with its last n slots free), merge the elements…

Companies: Amazon, Bloomberg, Google, Meta +2

Array · Sorting · Two Pointers

Last reported Apr 2026

Next Permutation

Rearrange the array in-place to produce the lexicographically next greater permutation (using only O(1) extra space); if no larger permutation exists, reorder it to the…

Companies: Amazon, Bloomberg, Meta, Microsoft

Array · Two Pointers

Last reported Apr 2026

Move Zeroes

Rearrange the array in-place so all zeros are moved to the end while preserving the relative order of non-zero elements, without using extra storage. Aim…

Companies: Amazon, Google, Meta, Microsoft

Array · Two Pointers

Last reported Apr 2026

Permutation in String

Check whether any substring of s2 of length |s1| is a permutation of s1 (i.e., has the same character multiset). The core challenge is to…

Companies: Apple, Meta

Hash Table · Sliding Window · String · Two Pointers

Last reported Mar 2026

Candy Crush

Given an m×n board of integer "candies," repeatedly find and remove any horizontal or vertical runs of ≥3 identical candies, let the remaining candies fall…

Companies: Meta, Microsoft, Roblox

Array · Matrix · Simulation · Two Pointers

Last reported Feb 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

Longest Mountain in Array

Find the length of the longest contiguous "mountain" subarray — a strictly increasing sequence immediately followed by a strictly decreasing sequence with length ≥ 3…

Companies: Oracle, TikTok

Array · Dynamic Programming · Enumeration · Two Pointers

Last reported Nov 2025

Interval List Intersections

Given two sorted, pairwise-disjoint lists of closed intervals, return all non-empty intersections between intervals from the two lists. Because each list is ordered and…

Companies: Meta, Verkada

Array · Sweep Line · Two Pointers

Last reported Sep 2025