Coding & Algorithms Interview Questions
Practice 2,970 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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"Discovered PracHub 10 days before my interview. By day 5, I stopped being nervous. By interview day, I was actually excited to show what I knew."
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Count All-One Square Submatrices
Given an n x n binary matrix, count how many square submatrices contain only 1s. A square submatrix can have any side length from 1 to n. Example: `te...
Compute exclusive execution time from logs
Problem You are given execution logs from a single-threaded CPU that runs n functions labeled 0..n-1. The CPU can run only one function at a time. A f...
Find best downhill ski run from a start
You are given an R x C grid of integers representing elevations. A skier starts at a given cell (sr, sc). From a cell, the skier may move up/down/left...
Validate whether a given sequence is a Hamiltonian path
You are given strArr, an array of three strings describing an undirected graph and a proposed vertex visit order: 1. strArr[0]: a comma-separated list...
Sample a string by real-valued scores
You are given: - A list of strings texts (e.g., user comments), length n. - A list of floating-point scores scores of length n, where each score can b...
Implement follow graph with snapshots
Problem You are building an in-memory social network relationship store that supports time-travel queries. Users are identified by integers. A directe...
Implement a type-based mutex for tasks
Problem You are given a multithreaded task runner. Each task has: - task_id: int - task_type: "gen" | "score" - duration: int (seconds) Each task runs...
Compute minimum rooms for meeting schedule
Problem You are given a list of meetings, where each meeting is represented as a pair of integers [start, end] (with start < end) indicating the meeti...
Implement Notification Rate Limiter
Implement should_send_notifications(user_id, timestamp) -> bool. You are given two mappings: - each user_id belongs to exactly one team_id - each team...
Populate next pointers in a perfect binary tree
You are given a perfect binary tree (all leaves at the same level; every internal node has two children). Each node has fields left, right, and next. ...
Implement Cache and Rotate Matrix
Solve the following two independent coding tasks. Task 1: Implement an LRU Cache Design a data structure LRUCache that stores integer keys and integer...
Implement Sliding Windows and LRU Cache
You are given two coding tasks. Task 1: Longest Subarray of Ones Given a binary array nums and an integer k, return the maximum length of a contiguous...
Implement a Cursor-Based Text Editor
Implement an in-memory text editor that maintains a mutable string and a cursor position between characters. The editor starts with an empty document ...
Review Preprocessing Code and Tests
You are reviewing a small Python preprocessing codebase during an interview. You do not need to write code. Part A: Environment and execution A shell ...
Design refundable transaction ledger and prioritization rules
Design and implement a transaction ledger that ingests a stream of records where each record is either a payment or a refund. Each payment has {id, us...
Minimize changes for k-periodic palindrome
Question Given a string currentPassword (length N) and an integer k (1 ≤ k < N, N ≤ 2·10^5, lowercase letters, N divisible by k), find the minimum num...
Minimize travel cost with two cities
You are scheduling candidates to attend an onsite interview. Each candidate i can fly to New York for cost c1[i] or to San Francisco for cost c2[i]. C...
Find Earliest Fully Connected Time
You are given n people labeled 0 to n - 1 and a list of friendship logs. Each log has the form (timestamp, personA, personB, action), where action is ...
Solve four coding problems
The interview included four independent coding problems: 1. Longest all-healthy service streak You are given the daily health-check results for mul...
Compute Inherited Role Privileges
You are given n roles. The array initialPrivileges has length n, where initialPrivileges[i] is the list of privileges directly assigned to role i. You...