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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Apply bitwise tricks for performance
For an integer-heavy inner loop, propose bit-level optimizations that reduce branches and memory traffic: e.g., population count usage, fast modulo by...
Detect runs and collapse a numeric grid
You are given an m x n grid of digits (0– 9). Phase 1: Find every horizontal or vertical run of length ≥ 3 consisting of the same digit. For each run,...
Implement hostname-restricted web crawler
Implement a single-threaded web crawler that, given a starting URL startUrl and an interface getUrls(url) that returns all hyperlinks on the page at u...
Solve word count, node, segmentation, stock tasks
You have four tasks: 1) Count words with explicit rules: Given a text document, return the number of words. First define precisely what qualifies as a...
Find first error and propagate failures
You are given a chronological log history where each entry is a string prefixed with one of [Info], [Warn], or [Error]. Two invariants hold: ( 1) once...
Implement weighted random choice
Implement a simplified version of np.random.choice without calling the built-in function. You are given an array items of length n and an optional pro...
Find max min-plus-max over all subarrays
You are given an array arr of n integers. A subarray is a contiguous non-empty segment of the array. For any subarray arr[l..r] (0-indexed), define: \...
Implement cheapest itinerary with date filters
Implement a function that computes the cheapest itinerary from a given origin to a destination using a list of flights, where each flight has (id, sou...
Simulate pouring water onto a 1D terrain
You are given a 1D terrain represented by an integer array heights, where heights[i] is the height of the column at index i. Part 1 — Render terrain W...
Maximize funds with capital-gated projects
You start with initial funds W and may undertake at most K projects. Each project i has a required capital C[i] and yields profit P[i]; you can only s...
Compute sum of longest positive subarray
Given an integer array that may contain positive and negative numbers, find the sum of the longest contiguous subarray consisting only of positive num...
Solve two DS&A optimization problems
Problem 1 — Maximize alternating-sum over four array partitions: Given an integer array arr[1..n] (1-based). Choose indices a, b, c with 1 ≤ a ≤ b ≤ c...
Simulate Grid Infection
Implement a grid infection simulator. Base problem: - You are given a 2D grid. - X means infected. - . means healthy. - Each day, every currently infe...
Infer Generic Return Types
Build a small type-inference engine for a toy language. Do not parse raw strings; the input is already constructed as Python objects. Type model: - Pr...
Decrypt a twice-encrypted message using known pairs
Three people pass notes A → B → C → A. Notes are encrypted using a character-substitution cipher (a one-to-one mapping per character). You are given t...
Track Expiring GPU Credits
Implement a GPU credit tracking system that processes time-stamped events arriving out of order. Operations: - add_credit(amount, start_time, duration...
Check if two-group seating is possible
Given an undirected graph represented as an adjacency list where adj[i] lists the indices of guests who know guest i, determine whether all guests can...
Validate word abbreviation and reconcile two abbreviations
Implement a function isValidAbbreviation(word: string, abbr: string) that returns true if abbr is a valid abbreviation of word, where a positive integ...
Reconstruct a tree from two traversals
Given two arrays representing the preorder and inorder traversals of a binary tree with unique values, reconstruct the tree and return its root. Achie...
Implement DelayQueue with Idempotent Task Execution
Scenario Message broker offers DelayQueue where tasks execute at future timestamps, ensuring idempotency on duplicate IDs. Question Implement a delay ...