Coding & Algorithms Interview Questions
Practice 2,960 real Coding & Algorithms interview questions for 2026. Coding & Algorithms interview questions for top tech firms like Meta, Amazon, Google, Uber, and TikTok — real questions from actual interviews with detailed solutions — to power your interview preparation. This collection is sharply focused on algorithmic patterns (arrays, strings, sliding windows, trees/graphs, dynamic programming, greedy, two-pointers, and hashing), clean, review-ready code, and the explanation skills that distinguish hires. In 2026 expect familiar medium-to-hard problems plus newer twists: AI-enabled or multi-file coding rounds at some companies, more emphasis on explainability and edge-case reasoning, and occasional real-world performance constraints (streaming, concurrency, memory limits). Interviewers evaluate problem framing, algorithm choice, complexity trade-offs, test-case thinking, and communication under time pressure. Best prep mixes pattern-based practice, timed mock interviews, code-review style polishing, and rehearsed explanations of complexity and tradeoffs. Focus your last-mile prep on writing correct, readable code quickly and on explaining why your solution is robust and efficient for production scenarios.
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Implement idempotent request handling with idempotency keys
Problem You are implementing an API endpoint (e.g., POST /charge) that must be idempotent using an Idempotency-Key. Design and implement an in-memory ...
Count changed nodes between two menu trees
You maintain a merchant menu as a rooted tree. Each node represents a menu item/category and has: - key (string, unique among siblings) - value (integ...
Simulate pouring water onto terrain
Problem You are given an integer array heights representing a 1D terrain (each index is a column height), an integer V (units of water), and an index ...
Find the longest palindromic substring
Problem Given a string s, find the longest contiguous substring of s that is a palindrome (reads the same forward and backward). Input - A string s co...
Find right-side view of binary tree
You are given the root of a binary tree. From the right side of the tree, at each depth you can see exactly one node: the rightmost node at that depth...
Implement two-pointer unique-pair sum search
Given a nondecreasing integer array nums and an integer target, return all unique value pairs [a, b] with a <= b such that a + b == target. Use the tw...
Evaluate a Piecewise Linear Function
You are given an ordered list of 2D points [(x1, y1), (x2, y2), ..., (xn, yn)]. Connecting each consecutive pair of points forms a piecewise linear fu...
Implement logger and card ranking
This coding round contains two independent implementation tasks. Task A: Implement a configurable logger Implement a Logger component that accepts tex...
Place Non-Attacking Queens
Given an integer n, return all valid configurations for placing n queens on an n x n chessboard so that no two queens attack each other. A queen attac...
Solve BST and Grid Query Problems
Solve the following coding problems. Problem A: Find the kth largest value in a BST You are given the root of a binary search tree and an integer k. R...
Implement a Least-Recently-Used Cache
Design and implement an in-memory least-recently-used cache. Requirements: - The cache is initialized with a positive integer capacity. - Implement ge...
Implement a Flappy Bird Jump Agent
Implement a function should_jump(state) -> bool for a simplified Flappy Bird game. The bird has a fixed horizontal position bird_x and a vertical posi...
Optimize a SQL query plan tree
Problem You are given an in-memory representation of a SQL query plan as a tree of nodes (a relational algebra plan). Each node is one of: - Scan(tabl...
Compute minimum path sum in a triangle
Given a triangle of integers represented as a list of rows, find the minimum path sum from the top to the bottom. - From row r and index c, you may mo...
Compute distance-sum from every tree node
Problem You are given an undirected tree with n nodes labeled 0..n-1 and a list of n-1 edges. The tree is connected and contains no cycles. For each n...
Write SQL for car rental utilization by city
SQL / Data Query Prompt (Car Rental) You are given four tables: user - user_id location - location_id - city car - car_id - car_size (e.g., compact, m...
Answer static and streaming Top-K queries
Top-K in static and streaming settings (3 variants) You are given integers and asked to answer Top-K queries under three different scenarios. Variant ...
Solve palindrome and list tasks
You are asked to solve two coding problems. 1. Build the shortest palindrome by prepending characters: Given a string s, add characters only to the fr...
Compute triangle min path and dice stopping stats
You are given two independent interview questions. 1) Triangle minimum path sum (DP) Given a triangular array triangle with n rows, find the minimum p...
Solve four classic algorithm problems
You are given four independent coding tasks. For each task, implement the required function. --- Problem 1: Zigzag level-order traversal of a binary t...