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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Reverse a singly linked list robustly
Reverse a Singly Linked List In-Place Context: You are given the head of a standard singly linked list (each node has value and next). Implement and e...
Find single element when others repeat k times
You are given a sorted array of integers nums in non-decreasing order, and an integer k ≥ 2. Every value in nums appears exactly k times in a row, exc...
Determine Straight Flush
Implement a function that determines whether a set of poker cards contains a straight flush. You are given a list of unique playing cards. Each card h...
Add two binary strings
You are given two binary strings a and b (each consisting only of characters '0' and '1'). Return their sum as a binary string. Input - a: string, len...
Implement solutions to several coding tasks
You are given several independent coding interview tasks. Solve each with the required time/space complexity. Problem 1: Find the minimum in a rotated...
Implement lazy array and KV store
You are asked two coding problems in the same interview round: 1. Implement a lazy array abstraction - Create a LazyArray<T> that wraps an input li...
Design robot path boundedness with repeats
You are given a 2D grid with a set of blocked cells (obstacles) and a robot starting at (0, 0) facing north. The robot executes a finite instruction s...
Design an in-memory database with TTL and backups
You are asked to implement a small in-memory “database” that evolves across 4 parts. In each part you may reuse your previous code and only add/extend...
Implement a Cache Snapshot Printer
Implement an LRU-style cache and a snapshot-printing feature. The cache stores key-value pairs and has a fixed capacity. It should support normal cach...
Solve three algorithmic OA tasks
Task 1 (Odd-frequency string): Given an integer N in [1..200000], write an algorithm that returns any length-N string of lowercase letters (a–z) such ...
Compute shortest path to collect all keys
You are given an m×n grid containing walls (#), open cells (.), a single start cell (@), up to six keys labeled 'a'–'f', and matching doors 'A'–'F' th...
Implement iterators and write tests in Java
In Java, write everything from scratch (no IDE scaffolding): 1) Define a generic Iterator<T> interface with hasNext() and next(). 2) Implement ArrayIt...
Design time-based key-value store
Design an in-memory key-value store that supports time-based lookups. Operations Implement a class (or module) with the following methods: 1. set(key,...
Maximize profit from one or many stock trades
You are given an integer array prices where prices[i] is the price of a stock on day i (0-indexed). Answer the following two subproblems: 1. Single tr...
Compute square root to 1 decimal
Problem Given a non-negative real number x, implement a function sqrt1dp(x) that returns \(\sqrt{x}\) rounded (or truncated—clarify with interviewer) ...
Find LCA in a tree and extend to a DAG
Part A — LCA variant in a rooted tree You are given a rooted tree with n nodes labeled 0..n-1. Input: - parent[i] for each node i (parent[root] = -1)....
Solve three coding problems
The interview note described the following coding questions: 1. Find the N-th license plate in lexicographic order - A license plate has exactly 6 ...
Solve string merge and grid path tasks
Question Given two equal-length strings s1 and s2, create a new string by iterating i = 0 … n-1, comparing s1[i] with s2[n-1-i]: append s1[i]; if the ...
Implement a match-3 board resolver
Question Implement a match-3 board resolver (the core loop of a "candy crush"-style game). You are given an m×n grid of cells. Each cell holds a value...
Format messages with paginated suffixes
You are given a message string s and an integer width w. Split s into multiple chunks, preserving character order, and append a suffix "i/n" to each c...