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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Handle multi-source string matching and tagging
Question Given an LLM output string and a list of source strings, design an algorithm to count how many times each source appears in the output. Exten...
Solve diverse LeetCode algorithm problems
Question LeetCode 695. Max Area of Island LeetCode 380. Insert Delete GetRandom O( 1) LeetCode 19. Remove Nth Node From End of List LeetCode 1004. Max...
Count deletions making array fair
Question LeetCode 1664. Ways to Make a Fair Array – Given an integer array nums, count the indices whose removal results in the sum of elements at eve...
Review Python geodata code
Question You are given a Python codebase that performs geolocation data processing. Conduct a thorough code review: identify readability, correctness,...
Reverse a linked list
Question LeetCode 206. Reverse Linked List — Given the head of a singly linked list, reverse the list and return the reversed list. https://leetcode.c...
Find Top K Frequent Elements
Question LeetCode 347. Top K Frequent Elements – given an integer array nums, return the k most frequent elements. Initial requirement: return the top...
Reconstruct tree from inorder and postorder
Given two arrays representing the inorder and postorder traversals of a binary tree with unique values, reconstruct the original binary tree and retur...
Detect runs and answer suffix queries
Given an array of comparable elements a[0..m-1] and an integer N: 1) Write a function that returns the maximum length of any run of consecutive equal ...
Find index of first unique character
Given a string s, return the index of the first character that appears exactly once; if none exists, return -1. Assume s may include both lowercase an...
Design a Resumable Iterator with Checkpoint and Restore
Design a resumable iterator: an iterator that can serialize its current position into a compact, opaque checkpoint and later be reconstructed from tha...
Design a temporal key-value store with historical reads
Implement a key–value store supporting set(key, value, timestamp) and get(key, timestamp) -> the value at the greatest timestamp ≤ the given timestamp...
Track article votes and last three flips
Problem Design an in-memory data structure for voting on articles. Users can vote on an article with either: - Thumbs up - Thumbs down - No vote (user...
Compute minimum-cost service cover
You are given: ( 1) a list of rental service packages, where each package contains a set of services (strings) and a non-negative price, e.g., [(["wif...
Find longest common subsequence length
Given two strings s and t, compute the length of their longest common subsequence (LCS). A subsequence is obtained by deleting zero or more characters...
Maximize minimum value after k decrements
You are given an integer array vulnerabilities of length n, where vulnerabilities[i] is the initial security score of server i. You must perform exact...
Implement a parallelized sort
Problem: Parallelized Sort (Shared-Memory) Implement a function that sorts an array using parallelism. Task Write a function (language of your choice)...
Find longest run of identical consecutive shows
Given an array shows of integers, find the maximum length of a contiguous run where all values are equal. Function signature - Input: shows: List[int]...
Find path between nodes in Fibonacci tree
You are given a recursively defined Fibonacci tree F(k): - F(0) is a single node. - F(1) is a single node. - For k >= 2, F(k) consists of: - a root ...
Build a time-based key-value store
Problem Design a data structure that stores multiple values for the same key at different timestamps, and can retrieve the most recent value as of a g...
Remove shortest subarray to sort array
Given an integer array nums (length up to 2×10^5), return the shortest subarray [L,R] you can remove so that the remaining elements form a non‑decreas...