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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Merge Two Sorted Lists
You are given the heads of two singly linked lists, each already sorted in non-decreasing order. Merge them into one sorted linked list and return the...
Resolve routing-number to bank mapping
You are given bank-routing data coming from one or more JSON sources. Each source provides a list of records like: `json { "routing": "026009593", "ba...
Implement stack variants and upward path sum
Question Answer the following coding questions. They progress from augmented stacks to streaming statistics to tree path reasoning. 1. MinStack — Desi...
Count nonnegative buy/sell sequences
You must perform exactly 2n unit trades starting with 0 shares and ending with 0 shares. Each trade is either a buy (+1 share) or a sell (−1 share), a...
Implement a timestamped map
Implement an in-memory timestamped map. Support these operations: - put(key, value, timestamp): store value for key at the given integer timestamp - g...
Remove minimum invalid mixed brackets
Given a string s containing letters and bracket characters from the set (), [], {}, remove the minimum number of bracket characters so that the result...
Count islands by requested sizes
You are given a 2D grid of characters '0' and '1', where '1' represents land and '0' represents water. An island is a maximal group of horizontally/ve...
Return a topological ordering of a graph
Problem: Output a topological ordering Given a directed graph with n nodes labeled 0..n-1 and a list of directed edges edges, return a topological ord...
Design O(1) cache and moving average
Problem You are asked two coding questions: 1) O(1) cache data structure Design a data structure that supports the following operations in O(1) averag...
Compute minimal operations and optimal server pairing
You are given two independent coding problems. Problem 1: Minimum range-increments to make an array nondecreasing Given an integer array power of leng...
Schedule dependent services with layered startup
You are given N services and dependency pairs (u -> v) meaning u must start before v. 1) Produce a valid startup order if one exists; otherwise detect...
Design a Randomized Multiset
Implement a data structure for integers that allows duplicate values and supports the following operations in expected O(1) time: - insert(val): Add o...
Approximate Pi from Random Points
You are given an array pts of points in the unit square. Each point is represented as an array of two numbers [x, y], where 0 <= x <= 1 and 0 <= y <= ...
Minimize batches and allocate riders by time
Coding prompts (same interview round) 1) Minimum number of batches for time points You are given a list of event time points (integers), e.g. [1, 3, 5...
Solve palindrome and missing-number variants
You are asked to solve two coding problems and analyze the time and space complexity of each. 1. Palindrome check Given a string s, determine whe...
Implement logger and card ranking
This coding round contains two independent implementation tasks. Task A: Implement a configurable logger Implement a Logger component that accepts tex...
Build Event Notification Engine
You are implementing part of a marketing engine for an event marketplace. Assume the following data is available: - Customer: id, city, birth_month, b...
Choose fastest way to transfer 2 TB
You need to transfer a 2 TB dataset to someone located in San Francisco as fast as possible. - What transfer method(s) would you choose and why? - St...
Remove duplicates from a singly linked list
You are given the head of a singly linked list of integers. Modify the list in place so that it contains only the first occurrence of each value (i.e....
Implement a versioned recipe management system
You are asked to implement an in-memory Recipe Management System (similar in difficulty to a simple banking/in-memory DB exercise). The system support...