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

Remove All Adjacent Duplicates in String II

Given a string s and integer k, repeatedly remove any run of k equal adjacent characters until no more removals are possible and return the…

Companies: Amazon, Apple, Meta, Oracle +2

Stack · String

Last reported Sep 2026

Simplify Path

Given an absolute Unix-style path, produce its canonical simplified form by collapsing multiple slashes and resolving "." (current dir) and ".." (parent dir) references. This…

Companies: Meta, NVIDIA, Roblox, Snowflake

Stack · String

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

Decode String

Decode a string containing nested repeat patterns of the form k[encoded_string], expanding each bracketed segment k times (k may be multi-digit) possibly with multiple nesting…

Companies: Bloomberg, Coupang, Google, Microsoft +4

Recursion · Stack · String

Last reported Aug 2026

Final Prices With a Special Discount in a Shop

For each price, compute the final cost as price minus the first subsequent price to its right that is <= it (or the same price…

Companies: Uber, Walmart

Array · Monotonic Stack · Stack

Last reported Aug 2026

Flatten Nested List Iterator

Given a nested list where elements may be integers or sublists, implement a NestedIterator with next() and hasNext() that returns all integers in depth‑first, left‑to‑right…

Companies: Adobe, LinkedIn

Depth-First Search · Design · Iterator · Queue

Last reported Aug 2026

Valid Parentheses

Check whether a string of parentheses/brackets is valid by ensuring every closing bracket matches the most recent unmatched opening bracket and the types and nesting…

Companies: Amazon, Apple, Bloomberg, Google +9

Bracket Sequences · Stack · String

Last reported Aug 2026

Valid Parenthesis String

Determine whether a string containing '(', ')', and '*' (where '*' can represent '(', ')', or empty) can be assigned so the parentheses are balanced…

Companies: Apple, Microsoft, Oracle

Bracket Sequences · Dynamic Programming · Greedy · Stack

Last reported Jul 2026

Min Stack

Design a stack supporting push, pop, top, and getMin operations all in O(1) time. The core challenge is to maintain and update the current minimum…

Companies: Expedia, Snowflake

Design · Stack

Last reported Jun 2026

Next Greater Element I

Given nums1 as a subset of nums2, for each element in nums1 return the first greater element that appears to its right in nums2 (or…

Companies: Flipkart, Microsoft

Array · Hash Table · Monotonic Stack · Stack

Last reported Jun 2026

Palindrome Linked List

Companies: eBay, Meta, Microsoft

Linked List · Recursion · Stack · Two Pointers

Last reported May 2026

Basic Calculator III

Evaluate a string arithmetic expression containing integers, +, -, *, /, parentheses and unary signs, respecting operator precedence and parentheses. The challenge is to parse…

Companies: Google, Intuit, Meta

Math · Recursion · Stack · String

Last reported May 2026

Longest Valid Parentheses

Find the length of the longest well-formed (balanced) parentheses substring in a string of '(' and ')', handling nested and adjacent valid segments; this typically…

Companies: Amazon, Meta, Microsoft, Uber

Bracket Sequences · Dynamic Programming · Stack · String

Last reported Apr 2026

Design Browser History

Implement a BrowserHistory class that supports visiting URLs (which clears any forward history), moving back or forward up to a specified number of steps, and…

Companies: Amazon, Bloomberg, Chime

Array · Data Stream · Design · Doubly-Linked List

Last reported Apr 2026

Buildings With an Ocean View

Given an array of building heights, return the indices of buildings that have an unobstructed view to the ocean on the right (i.e., no building…

Companies: Anduril, Meta

Array · Monotonic Stack · Stack

Last reported Apr 2026

Asteroid Collision

Given signed integers for asteroid sizes and directions, determine which asteroids remain after sequential collisions where only opposite-moving neighbors (positive then…

Companies: Amazon, D. E. Shaw, JPMorgan Chase, Meta +2

Array · Simulation · Stack

Last reported Mar 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

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

Beautiful Towers II

Choose heights within [1, maxHeights[i]] that form a mountain (nondecreasing to a single peak then nonincreasing) to maximize the total sum. Core challenge: for each…

Companies: Bloomberg, Expedia

Array · Monotonic Stack · Stack

Last reported Sep 2025

Binary Tree Inorder Traversal

Return the node values of a binary tree in inorder (left → root → right) sequence. The recursive solution is trivial; the follow-up asks for…

Companies: Anduril, Meta, Oracle

Binary Tree · Depth-First Search · Stack · Tree

Last reported Jul 2025

Add Two Numbers II

Companies: Meta, Pinterest

Linked List · Math · Stack

Last reported May 2025