Coding & Algorithms Interview Questions
Practice 3,013 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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Join tables to map userId to name
Problem You are given three tables represented as 2D string arrays (each row is a record, no headers). You need to produce a mapping from userId → cus...
Detect overlap of two linked lists with cycles
You are given the heads of two singly linked lists headA and headB. Each list may be: - A standard acyclic linked list, or - A cyclic linked list (con...
Merge overlapping intervals
Given an array of closed intervals intervals, where each interval is [start, end] and start <= end, merge all overlapping intervals and return an arra...
Return sorted values after quadratic transform
Problem You are given a sorted integer array nums (non-decreasing order) and integers a, b, c that define a quadratic function: \[ f(x) = ax^2 + bx +...
Implement a rate limiter at scale
Problem Design and implement a rate limiter that enforces request limits per key (e.g., per user ID or API key). Requirements - Implement allow(key, t...
Maximize the minimum value along a grid path
You are given an m x n integer matrix A. You start at the top-left cell (0,0) and want to reach the bottom-right cell (m-1,n-1) by moving only in 4 di...
Group strings that are anagrams
Problem: Group anagrams Given an array of strings strs, group the strings that are anagrams of each other. Two strings are anagrams if they contain th...
Determine whether a word exists in a letter grid
Given an m x n grid of characters board and a string word, determine whether word can be constructed from sequentially adjacent cells. Rules: - Adjace...
Minimize total distance to a store
Question 1: Choose a CVS location to minimize total distance You are given an M x N grid grid containing only 0 and 1. - grid[r][c] = 1 means there is...
Solve order-statistics and XOR-triplet problems
You are given two separate algorithmic problems. Problem 1: Count smaller elements to the right Given an integer array nums of length n, for each inde...
Solve string transform and min-move sorting
Problem 1: "Goat Latin"-style string transformation You are given a sentence s consisting of words separated by single spaces. Transform it into a new...
Coordinate workers across two exclusive targets
You are given two exclusive resources (targets) labeled "A" and "B". You need to start N = 10 parallel workers (e.g., processes or threads), each of w...
Solve three string/stack/backtracking problems
You are given three independent coding tasks (solve each one). Unless otherwise stated, implement a function with the described input/output. Problem ...
Generate combinations and permutations
Given two integers n and k, where 1 <= k <= n, write code for two related tasks using the numbers 1 through n: 1. Generate all unique combinations of ...
Design KV store with sliding-window average QPS
Problem Design an in-memory key–value store that supports mutation operations and can report the average QPS (queries per second) over a recent time w...
Compute last-5-minute QPS in memory
Problem You are building a lightweight in-memory component that tracks the query load (QPS) of a service. Design a data structure with two operations:...
Choose optimal guesses for green-only Wordle
Problem You are playing a simplified 5-letter word guessing game. - There is a hidden secret word of length 5. - You have a dictionary of valid 5-lett...
Implement minimal-cost overtime/contractor allocation
You must cover H extra engineering hours this week at minimum cost using employee overtime and optional contractors. Each employee i has a maximum ove...
Maximize outfits with distinct colors
You're given counts of items by color; each outfit must contain exactly 3 items, all of distinct colors. You cannot reuse items. Input formats: either...
Implement longest increasing subarray with one deletion
Given an array of integers nums, return the length of the longest strictly increasing contiguous subarray you can obtain by deleting at most one eleme...