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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Compute buffet revenue with capacity and waiting
A casino buffet has a maximum capacity capacity (number of customers that can be seated at once). You are given: 1) prices: an array where prices[i] i...
Return dictionary words matching a prefix
You are given a list of strings words (a dictionary) and a string prefix. Return all words in words that start with prefix. Clarifications/constraints...
Explain C++ vector, unordered_map, and virtual functions
In C++, explain: - The amortized and worst-case time complexity of vector::push_back, and how capacity growth/expansion is implemented (growth factor,...
Implement concurrent structures and debug queue code
The coding rounds covered several implementation and debugging tasks: 1. Implement an LRU cache that supports get(key) and put(key, value) in constant...
Implement task queue with insert, delete, execute
Problem: Task manager with insert/delete/execute-next Design a data structure to manage executable tasks. Each task has: - taskId (unique) - priority ...
Find bounding boxes of connected houses
You are given a 2D grid representing a map, where each cell is either 1 (part of a house) or * (empty). A house is a maximal group of 1 cells connecte...
Solve Matrix, Tree, Nested, LCA, Maze Tasks
Answer the following independent coding tasks. For each task, implement a clean API, handle edge cases, and analyze time and space complexity. 1. Trav...
Build a React team builder with role constraints
Problem (React) Implement a small React UI that allows a user to build a team from a list of players. UI - Left panel: a list of available players. Ea...
Determine escape path with blockers and spreading fire
You are given a 2D grid representing a grassland. - Each cell is one of: - S: start - T: target - .: free cell - #: blocked cell (cannot enter...
Implement a fixed-capacity generic circular buffer
Design a data structure that stores generic elements T with the following properties: - FIFO semantics (queue): pop() returns the oldest element. - pu...
Check perfect square using binary search
Perfect Square Check (Binary Search) Given a positive integer n, determine whether it is a perfect square (i.e., there exists an integer x such that x...
Delete nodes in linked list and binary tree
You are asked to solve two short coding tasks. You may assume standard node definitions: - Singly linked list node: val, next - Binary tree node: val,...
Implement encode/decode for list of strings
You are given a list of strings (may include digits and symbols). Implement two methods: - encode(List<String> input) -> String: converts the list int...
Solve string grouping and tree right-view problems
Problem 1: Group words that are anagrams You are given an array of strings words. Two strings are anagrams if they contain the same characters with th...
Design O(nm) grouping of rearranged strings
Given an array of strings, group together words that are permutations of the same characters. Provide a baseline solution that sorts each word (O(n · ...
Compute dot product of sparse vectors
Problem You need to compute the dot product of two sparse vectors of the same dimension. Each vector is provided as a list of non-zero entries sorted ...
Solve transaction aggregation and search tasks
Complete the following coding tasks: (a) Given a list of transactions, each with userId and amount (credits positive, debits negative), compute the fi...
Compute ring window max and deletion indices
Part A — Ring window maximum: You are given n computers arranged in a circle, represented by an array of bits (1 = on, 0 = off), and an integer k (1 <...
Implement 64-bit modular exponentiation safely
Implement a function to compute (a^b) mod m where 0 ≤ a,b < 2^61−1 and 1 ≤ m < 2^61−1 using only 64-bit operations without overflow. Provide implement...
Optimize file reads for password validation
Given a multi-gigabyte credentials file on disk with one record per line in the format user_id,salt,password_hash (hex), implement validate(user_id, p...