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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"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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Find kth smallest and count stair-climbing ways
You are given two separate algorithm questions. A) Find the k-th smallest element in an array (no sorting) Given an integer array nums of length n and...
Validate hiring request under role constraints
Problem You are building a simple HR assignment validator for a platform with companies, employees, and job roles. When the system receives a request ...
Find two numbers summing to target without hashmap
Problem Given an integer array nums (length n) and an integer target, return the indices (i, j) such that: - i != j - nums[i] + nums[j] == target You ...
Serialize and deserialize a binary tree
Problem Design two functions to serialize and deserialize a binary tree. - Serialize: convert a binary tree into a single string. - Deserialize: recon...
Compute minimax grid path and network delay
Problem (two related shortest-path tasks) Part 1 — Minimize the maximum value along a grid path ("minimax" path) You are given an m x n integer grid H...
Solve tiling, probability, and nested-radical puzzles
You are given several independent math/coding puzzles. 1) Domino tiling a 2×N board You have a 2×N rectangle and an unlimited number of 1×2 and 2×1 do...
Solve two-sum variants at scale
Base task: Given nums = [3, 1, 2, 2, 4] and target = 4, return the 0-based index pair (i, j) with i < j such that nums[i] + nums[j] = target. If multi...
Implement sqrt with Newton vs binary search
Implement numerically robust square-root routines and analyze convergence Task 1 — sqrt_newton(x, tol=1e-12) Implement a Python function that returns ...
Compute and Rank by Jaccard Similarity
Implement two functions: (1) jaccard_similarity(s1, s2) that tokenizes by splitting on any non-alphanumeric character, lowercases, treats tokens as se...
Design and secure a REST inference API
Design a REST API for Image Inference with Grad-CAM You are designing a public REST API for an image-inference service that accepts large images and r...
Compute optimal matrix-chain multiplication order
Matrix Chain Multiplication: Optimal Parenthesization and Analysis You are given five matrices to multiply: A1 (10×30), A2 (30×5), A3 (5×60), A4 (60×2...
Design an in-memory filesystem and circular queue
Part A — Design an in-memory hierarchical file system. Requirements: - Support operations: ls(path), mkdir(path), createFile(path, content), appendToF...
Compute max team size with a core interval
You are given n employees’ working-time intervals, where employee i works during the inclusive interval [startTime[i], endTime[i]]. You want to form a...
Implement LRU cache and copy random list
Coding questions (two parts) Part A — Deep copy a linked list with random pointers You are given the head of a singly linked list where each node has:...
Find the Smallest String After One Decrement
You are given a string s consisting only of lowercase English letters. You must perform exactly one operation: 1. Choose one non-empty contiguous subs...
Compute total after discounting most expensive item
Problem You are given: - An array prices of length n, where prices[i] is the price of the i-th item. - An integer discountPercent (0 to 100). A promot...
Implement an LRU Cache
Problem: LRU Cache (LeetCode 146) Design and implement a Least Recently Used (LRU) Cache that supports the following operations in average O(1) time. ...
Solve four algorithmic problems
Solve the following coding tasks. For each, describe your approach, complexity, and handle edge cases. 1) Make parentheses string valid with minimal d...
Answer k-step ancestor queries in a rooted tree
You are given a rooted tree encoded as a parent array par[1..n] where: - Nodes are labeled 1..n. - par[i] is the parent of node i. - Exactly one node ...
Debug Tensor Conversion Bugs
You are given a small tensor utility library used in distributed numerical code. The implementation has several bugs related to aliasing, array conver...