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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Count Interior Islands After Flooding
You are given an m x n binary grid representing land and water. - 1 = land - 0 = water An island is a maximal group of land cells connected 4-directio...
Check palindrome number and next palindrome
Problem You are given a non-negative integer n. 1. Determine whether n is a palindrome in base-10 (it reads the same forward and backward). 2. Follow-...
Evaluate arithmetic expression using DFS
Given a string representing an arithmetic expression with non-negative integers, +, -, *, /, parentheses, and optional spaces, evaluate its value. Use...
Implement a per-user API rate limiter
You are building an API gateway that must enforce per-user rate limits. Task Implement a rate limiter with the following API: - RateLimiter(int maxReq...
Find missing numbers in sequences
You are given several number sequences (integers and/or rational numbers). Each sequence contains exactly one missing term written as ?. For each sequ...
Find largest subset sharing a common digit
You are given a list of two-digit integers (each from 10 to 99, inclusive). You want to select as many numbers as possible in one selection such that:...
Compute Products Excluding Each Index
You are given an integer array nums of length n. Return an array answer such that answer[i] equals the product of every element of nums except nums[i]...
Implement Buffer Parsers and Generic Map Class
In C++, complete the following two independent implementation tasks. 1. Sequential buffer reader You are given a raw byte buffer and a current poin...
Merge Sorted Arrays In Place
You are given two non-decreasing integer arrays. - A has length m + n. - The first m elements of A are valid sorted numbers. - The last n elements of ...
Add two big integers from digit lists
You are given two non-empty singly linked lists (or arrays) representing two non-negative integers. The digits are stored in reverse order, and each n...
Answer four string/array/battery coding questions
You are given four independent coding questions. Problem A — Uppercase vs lowercase count difference Given a string s (ASCII), count how many characte...
Compute winning probability on 1D dice walk
You are on an infinite 1D number line starting at position 0. Repeatedly roll a fair die that returns an integer uniformly at random from 1 to K (incl...
Find shortest transformation steps in a word graph
You are given two strings begin and end of the same length, and a list words of distinct strings (also same length). You can transform one string into...
Implement K-means and solve interval/frequency tasks
Task 1 — Describe/implement K-means clustering Given: - A data matrix X with shape (n_samples, d). - An integer k (number of clusters). Explain (or wr...
Implement plurality and majority voting
You are given an array votes of length n, where each element is a candidate identifier (string or integer). Implement two voting systems: 1) Plurality...
Count friend requests based on age rules
Problem You are given an array ages, where ages[i] is the age of the i-th person. A person of age A will send a friend request to a person of age B if...
Detect recurring transactions from a ledger
You are given a list of credit/debit card transactions. Each transaction has: - transaction_date (YYYY-MM-DD) - merchant (string) - amount (decimal, p...
Maximize min+max of contiguous subarray
You are given an array of n positive integers nums. Find a contiguous subarray that contains at least two elements and maximizes the value: > (minimum...
Rearrange array to maximize positive prefix sums
Problem You are given an integer array a of length n. You may rearrange the elements in any order. Define the prefix sums of a permutation p as: - pre...
Schedule Ready Tasks by Deadline
You are building a workflow scheduler. Each task has: - a unique task_id - an integer deadline - an optional list of prerequisite tasks that must be c...