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."
"I recently cleared Uber interviews (strong hire in the design round) and all the questions were present in prachub."
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Find a split-stay booking across listings
You are implementing a simplified split-stay search. You are given: - A desired trip interval [start, end), where dates are represented as integers (e...
Build a Pivot Table Aggregator
Implement a function that builds a pivot table from a list of records. Each record contains a row_key, a column_key, and a numeric value. Requirements...
Simulate and Construct Tournament Rankings
You are given a single-elimination tournament represented by an array of ranks. The array is a permutation of the integers 1..n, where a smaller numbe...
Implement Stratified Sampling by Country
You are given a large in-memory Python list named records, where each element is a dictionary with at least the following keys: - country: str - devic...
Solve Union-Find, Graph, and Stream Problems
Solve the following independent coding problems. 1. Merge Product Categories You are given a list of tuples (productA, productB). Each tuple means the...
Find balanced subarray and increasing tree path
You are given two coding problems. Problem 1: Longest balanced subarray (0/1) Given an integer array nums of length n where each element is either 0 o...
Determine validity after digit-constrained deletions
You're given a string S of length n consisting only of '(' , ')' , and digits '0'–'9'. For every digit at index i with numeric value v: ( 1) you must ...
Infer and justify non-trivial sequence patterns
Pattern Recognition: Next Terms and Missing Value Identify the rule governing each sequence or row and compute the missing value(s). Justify each answ...
Implement DFS with cycle detection and topo order
Implement DFS (recursive and iterative) with topo sort, cycle detection, and timestamps You are given a directed graph G with N nodes labeled 1..N and...
Implement robust k-means with k-means++ initialization
Implement from scratch in Python (no scikit‑learn) a function kmeans(X, k, max_iter=300, tol=1e-4, random_state=0) that returns (centroids, labels). R...
Check anagrams under real-world constraints
Given two strings s and t, determine whether they contain exactly the same multiset of characters (e.g., 'abc' and 'cab' → true; 'aab' and 'ab' → fals...
Implement CUDA-tiled matrix multiplication and explain architecture
CUDA FP32 GEMM Design Task Implement a high-performance CUDA kernel for matrix multiplication C = A · B where: - A is m×k, B is k×n, C is m×n - Data t...
Compress editor keystrokes into insert/delete/skip
You are implementing a simplified collaborative editor sync format. You are given: - An initial document string doc. - A list of user input operations...
Check if all substrings are anagrams of words
You are given a string s (letters only) and access to an English dictionary dict (a set of valid words). Return true if every contiguous substring of ...
Implement a Composable Event Recommendation Engine
Design and implement a flexible event recommendation engine in Java. You are given domain objects such as Event, Customer, Inventory, and a LocationSe...
Implement most frequent key without using max()
You are given the following Python class skeletons. The Parent class precomputes: - self.l: the original list - self.lf: a set of the stringified item...
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...
Design paint editor with undo/redo
Implement a simplified Paint editor that supports drawing on a 2D canvas and reverting changes using undo and redo operations. Canvas You are given a ...
Simulate a Turn-Based Two-Player Game
Design and implement a simulator for a two-player turn-based board game similar to tic-tac-toe. Requirements: - The game is played on an n x n board. ...
Solve Two Coding Interview Problems
You are asked to solve two independent coding problems. Problem 1: Evaluate Nested Math Expressions Implement a function that evaluates a string expre...