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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Compute Infection Time in a Grid
You are given an m x n grid where each cell is one of the following: - 0: empty - 1: healthy - 2: infected Every minute, each infected cell spreads th...
Calculate Jaccard Similarity Score for Two String Lists
Scenario During pair programming, the interviewer asks you to compare two lists of merchant tags and quantify their similarity. Question Implement a P...
Decide transform via one-to-one mapping
You are given two strings s and t of equal length over the lowercase English alphabet. In one step, you may pick any character x and replace all its o...
Compute Differences Between Catalog Trees
You are given two rooted catalog trees. Each node has a unique string key among its siblings and an associated value. Compare the two trees and return...
Compare two programs for equivalence
You are given two short programs (or functions) that process an integer array A (|A| ≤ 10^ 5). Determine whether they are functionally equivalent for ...
Implement Luhn-based card validation and inference
Question Implement a set of utilities for credit-card validation and inference using the Luhn checksum algorithm and standard brand patterns. Brand pa...
Cross-reference logs to flag spam numbers
You are given two data sets: ( 1) a call log containing phone numbers observed in calls and ( 2) a list of user reports where each entry is a phone nu...
Solve Merge Lists and Vertical Traversal
Two coding tasks were mentioned for a 40-minute round: 1. Merge multiple sorted linked lists: You are given an array of k singly linked lists, where e...
Design compressed vector and compute dot product
Problem You are given very long integer vectors where many adjacent elements repeat (e.g., long runs of the same value). Storing the full array is mem...
Find secret word with match-count feedback
Problem You are given a list of unique lowercase words, all of the same length (e.g., length = 6). One of these words is a secret word. You can intera...
Find minimum-latency path across dependent services
You are given a set of services and directed dependencies between them. Each dependency edge represents a call from one service to another with a know...
Implement an LFU cache with O(1) operations
Design and implement an LFU (Least Frequently Used) cache. The cache supports: - get(key): return the value for key if present, else return -1. - put(...
Compress vertices into uniques and indices
You are given an array of vertices (a 2D array). Each vertex may repeat. Implement a simple “compression” that produces: 1. unique_vertices: the list ...
Compute sums and maximum path in a tree
You are given a binary tree whose nodes store integer values. You must implement your own Node class (e.g., val, left, right). Task Write a function t...
Simulate 2048 and pack board into uint64
Problem: 2048 move simulation + board compression You are implementing part of the 2048 game on a fixed 4×4 grid. Part A — Simulate a move Given a 4×4...
Construct smallest number from I/D pattern
Problem You are given a string pattern consisting only of the characters: - 'I' meaning the next digit is increasing - 'D' meaning the next digit is d...
Compute sparse dot product and count islands
You are asked to solve two coding problems. Problem 1: Sparse vector dot product Given two vectors A and B of the same length n (potentially large, e....
Implement a thread-safe rate limiter
Design and implement a per-user API rate limiter. Requirements: - Method: boolean allow(String userId, long nowMillis) returns whether the request is ...
Find largest digit-sum bucket size
You are given two integers low and high (inclusive). Define s(x) as the sum of the decimal digits of x. For every integer x in [low, high], place x in...
Can one car serve all riders?
Given a list of passenger waiting intervals, determine whether a single car can serve all passengers without any scheduling conflict. Each interval is...