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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Implement bank account with cashback
Implement a bank account processor. Given an initial non-negative integer balance B and a list of operations (n up to 1e 5), apply each operation in o...
Design weighted random index picker
Design and implement a data structure that, given an array of positive integer weights w[0..n−1], supports pick() that returns index i with probabilit...
Convert Integer to Non-Adjacent Form
Implement toNAF(n) that converts an integer n (allow negative n) to its Non-Adjacent Form using digits from {-1, 0, 1} with no two adjacent nonzero di...
Design a no-repeat top-frequency music player
Design and implement a music player that receives song lists from new users and returns songs to play in frequency order without repeating a song in t...
Compute city skyline silhouette
Compute the outer silhouette of a 2D skyline. You are given n axis-aligned rectangular buildings; each building i is (Li, Ri, Hi) with 0 <= Li < Ri an...
Compute longest increasing path in a matrix
Given an m × n integer matrix, return the length of the longest path of strictly increasing values, where from each cell you may move only up, down, l...
Compute Available Offers per User
You are given a set of promotional offers and a CSV event stream read from standard input. Each Offer has the following fields: - name: string - start...
Solve median extremes and segment flips
Part A — Sliding-window median extremes: - Input: an integer k (1 ≤ k ≤ n) and an array nums of length n. - For every contiguous subarray of length k,...
Produce asymmetric side views of a binary tree
Given a binary tree, output two sequences: ( 1) Left-bottom-up view: for each depth, the first node visible when viewing the tree from the left side, ...
Implement an in-memory order book API
Problem Implement an in-memory limit order book for a single trading symbol. You do not need to implement order matching/execution—only store and main...
Solve array, tree, and maze problems
The onsite interview included the following algorithmic tasks: 1. Building visibility from the right: Given an integer array heights, where heights[i]...
Find smallest N for 5-and-21 sums
You are given two positive integers: 5 and 21. We say a positive integer x is representable if it can be written in the form \[ x = 5a + 21b \] for so...
Implement several string, tree, and BFS problems
You are given several independent coding tasks. Implement each as described. A) Print a root-to-target path with column indentation (binary tree) Give...
Compute capacities after site closures
You are given a nested dictionary redistribution where redistribution[closed_site][dest_site] equals the additional capacity required at dest_site if ...
Implement autocomplete with top-K suggestions
Implement an autocomplete component that, given a history of query strings with frequencies, returns the top K suggestions for an input prefix in real...
Find max-score path in weighted DAG
You are given a directed acyclic graph (DAG). Each node v has a score w(v). Each directed edge (u→v) has a nonnegative time cost t(u,v). There is a un...
Design a nested-list iterator
You are given a nested structure that can contain integers or further lists. Design an iterator over this structure that returns integers in left-to-r...
Compute exclusive times and call stack from logs
Design an algorithm that, given a single-threaded program's execution log, computes per-function exclusive durations and reconstructs the active call ...
Find next and closest palindromes
Given a non-negative integer represented as a string n (no leading zeros unless n == "0"), return the smallest palindromic integer strictly greater th...
Find horizontal cut balancing square areas
Given a 2D table with top-left origin (0, 0), you are provided a finite set of n non-overlapping, axis-aligned square cakes. Each square i has real-va...