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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Solve permutation successor and evaluate expressions
Part A: Given a sequence of integers that forms a permutation, rearrange it in-place to produce the immediate next sequence in lexicographic order. If...
Implement stack and interval algorithms with tests
Implement three coding tasks and design your own unit tests for each. 1) Validate Bracket String with a Stack - Input: a string s containing only '(',...
Solve matrix components, median, and traversals
1) Binary matrix component: Given an m x n grid of 0s (background) and 1s (objects), return the size of the largest connected component where connecti...
Find Maximum Envelope Nesting
You are given a list of envelopes, where each envelope is represented by [width, height]. One envelope can be placed inside another only if both its w...
Find Final Ball Holder
You are given an array receiver of length n, where friends are numbered from 1 to n. If friend i currently holds the ball, then after one second they ...
Find Shortest Clear Grid Path
Given an n x n binary grid, where 0 means open and 1 means blocked, return the length of the shortest clear path from the top-left cell to the bottom-...
Determine string transform via end-append moves
Given two strings s and t of equal length over lowercase English letters, in one move you may delete any character from s and append it to the end of ...
Find k closest values in a BST
Given a binary search tree with n nodes and a real target t, return k node values whose distances to t are smallest. Implement an algorithm with O(log...
Implement an unbiased array shuffle
Implement an in-place function shuffle(arr) in JavaScript that returns a uniformly random permutation of the input array. The algorithm must be unbias...
Minimize adjacent-color assignment cost
You are given H linear items (e.g., houses) and an H×C cost matrix where cost[i][c] is the cost of assigning color c to item i. Adjacent items cannot ...
Find lexicographically smallest string and elimination order
You remember two coding questions from an online assessment. Question 1: Return the lexicographically smallest string after a prefix/suffix reverse Yo...
Process time intervals and detect overlaps/gaps
You are given n time intervals representing debug log segments. Each interval has a start time, an end time, and an associated text message. - Each in...
Compute island size in grid
Given an m x n binary matrix grid of 0s (water) and 1s (land), where an island is a group of 1s connected 4-directionally, implement sizeOfIsland(grid...
Find longest substring with at least k repeats
Longest substring where each character appears at least k times You are given: - a string s consisting of lowercase English letters - an integer k Ret...
Compute distance of each node to a cycle
Problem You are given an undirected graph with n nodes labeled 0..n-1 and a list of edges. The graph is connected and contains exactly one simple cycl...
Maintain streaming median and loosemedian
Design a data structure for an online stream of positive integers supporting insert (x). After each insertion, output: (a) the median of all values se...
Solve swaps, graph paths, and movie DP
Design and implement solutions for three tasks derived from a HackerRank-style assessment. 1) Minimum swaps to reverse sort an array: - Input: an inte...
Find second-minimal word segmentation count
Given a string s and a dictionary D of non-empty words, define a 'segmentation' as splitting s into a sequence of words from D whose concatenation equ...
Decide palindrome within k deletions
Given a string s and integer k, decide whether s can be transformed into a palindrome by deleting at most k characters. Provide an algorithm to comput...
Design Minesweeper and Optimize Click Performance
Design a Minesweeper game. At game start, initialize an m×n board by randomly placing k bombs. Implement: ( 1) printBoard(): return a human-readable s...