Coding & Algorithms Interview Questions
Practice 3,469 real Coding & Algorithms interview questions for 2026. Covers companies like Meta, Amazon, Google, Uber, and Microsoft. Real questions from actual interviews with detailed solutions — ideal for focused interview preparation. Coding & Algorithms interview questions are the single most common technical gate for software engineering roles and are used to evaluate problem framing, algorithm selection, complexity trade-offs, correctness, edge-case reasoning, and clear communication under time pressure. Expect this category to appear in early technical screens and repeatedly across onsite loops at companies that weight it heavily (notably Meta, Google, and Amazon). Interviews will test arrays and strings, trees and graphs, dynamic programming, hashing and two‑pointer techniques, and the candidate’s ability to test and optimize code in a shared editor. Prepare with timed mock interviews, practice in the same editor you’ll use live, and build a progressive schedule that moves from fundamentals to medium/hard problems; typical candidates invest several weeks to a few months of focused practice depending on seniority and target company.
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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."
"I recently cleared Uber interviews (strong hire in the design round) and all the questions were present in prachub."
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Design in-memory payment and friendship system
Design and implement an in-memory payment system with simple social features. The system processes a sequence of requests that can: 1. Register a user...
Implement account scheduler with locking and LRU
Design a class AccountScheduler that manages the time-based availability of a fixed set of account IDs. Initialization You are given: - accounts: a li...
Compute longest increasing path in matrix
You are given an m x n grid (matrix) of integers grid, where m >= 1 and n >= 1. A path in the matrix is a sequence of cells where: - You may move from...
Count ways to decode digit string
You are given a string s consisting of digits '0' to '9'. The string encodes a message using the following mapping: - '1' → A, '2' → B, ..., '26' → Z....
Shuffle array using random integer API
You are given an array nums of length n representing a deck of distinct cards. You do not have access to a built-in shuffle function, but you are give...
Find longest duplicated substring
You are given a string s consisting of lowercase English letters. A substring of s is any contiguous sequence of characters, i.e., s[i..j) for 0 ≤ i <...
Group users by same last K watched movies
You are given a list of users' movie-watching histories. Each user’s history is an ordered list of movie IDs in the order they were watched (earliest ...
Implement integer division without using division
You are given two 32-bit signed integers dividend and divisor. Implement a function that divides dividend by divisor and returns the integer quotient,...
Validate complete binary tree
You are given the root of a binary tree. A complete binary tree is defined as a binary tree in which: 1. Every level, except possibly the last, is com...
Find first CIDR block covering IP
You are given: - A single IPv4 address as a string, e.g. "192.168.1.5". - A list of CIDR blocks (IPv4), each as a string in the form "a.b.c.d/x", wher...
Implement basic pagination for a list
You are given: - A zero-indexed array of items items (you can assume it fits in memory). - An integer pageSize > 0. Design and implement a pagination ...
Compute clock hand angle with seconds and milliseconds
You are given a time in the format "HH:MM", representing a 24-hour clock time with hours and minutes. Extend this to potentially include seconds and m...
Design data structure similar to LRU cache
You are asked to design and implement a data structure that behaves similarly to an LRU (Least Recently Used) cache, but with a small variation: - The...
Find largest digit-sharing subset
You are given an array of N integers. Each integer has exactly two decimal digits (i.e., each element is between 10 and 99 inclusive). You want to cho...
Implement basic calculator with four operations
Implement a basic arithmetic expression evaluator. Problem You are given a string s representing a mathematical expression containing non-negative int...
Implement stateful connection router simulator
You are implementing a simplified connection router / load balancer for a Jupyter-like multi-tenant server system. There are N target servers, indexed...
Maximize coins with tokens moving by +3
You are given a 1D board represented by a string s of length n. Each character is one of: - '.' — an empty cell - 'C' — a cell containing exactly one ...
Detect earliest collision among moving cars
You are given n vehicles with kinematics parameters. A “collision” means two vehicles occupy the same position at the same time. Assume continuous tim...
Compute Max Score From Up to 3 Categories
You are implementing a scoring function for a library summer reading program. Each book a student read is represented as a tuple (category: str, point...
Evaluate word-guess feedback with repeats
You are implementing feedback for a Wordle-like guessing game. Part 1 — Produce feedback for one guess You are given two strings of equal length guess...