Coding & Algorithms Interview Questions
Practice 2,950 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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Design Composable Event Recommendations
Build a flexible event recommendation engine for a ticket marketplace. You are given these domain objects and services: - Event(id, name, city, date) ...
Insert parentheses to minimize expression value
You are given a string expression of the form A+B, where A and B are non-empty strings of digits (no digit is '0'). You must insert exactly one pair o...
Explore an HTTP Maze
You are given an HTTP API that represents a maze-like forest. The entrance is available at GET /mirkwood. Each location in the forest is identified by...
Convert Samples into Event Intervals
You are given a time-ordered array samples, where samples[i] is the function name observed at integer timestamp i. Convert this trace into a list of e...
Count same-color squares in a character grid
You are given a 2D grid (matrix) of characters. Each character represents a color: cells with the same character are considered the same color. Formal...
Solve String Addition and Expression Evaluation
The interview included two coding problems: 1. Add numbers from character arrays - You are given two non-empty character arrays, where each array r...
Design a violation log analyzer
You are given an append-only list of violation events as tuples (id: string, policy: string, date: ISO-8601 string). Build an in-memory "Violation Log...
Maximize palindromic strings after character swaps
You are given an integer n and an array of n lowercase strings arr. Operation (can be performed any number of times): choose two different strings arr...
Design an In-Memory Database
Implement a simple in-memory database with a flexible, schema-less record model. Requirements: - Each record is a mapping from column_name to value. -...
Solve Sliding Window and Grid Search
In a Software Engineer phone screen, the candidate was asked to solve two coding problems. 1. Longest substring with at most k distinct characters ...
Select words to maximize unique characters
Problem You are given an array of strings words. You may choose any subset of these strings and concatenate the chosen strings in any order. Your goal...
Sort a nearly sorted array
Given an array of length \(n\) in which every element is at most \(k\) positions away from its location in the fully sorted order, design an algorithm...
Simulate document assignment to indexers
You are given a system with m parallel indexers (workers), numbered from 0 to m-1. Documents arrive over time and are placed in a processing queue. Ea...
Compute Inherited Role Privileges
You are given n roles. The array initialPrivileges has length n, where initialPrivileges[i] is the list of privileges directly assigned to role i. You...
Implement Memory Allocation and In-Memory Records
Solve the following two implementation problems. Problem A: First-Fit Memory Allocator You are given a contiguous block of memory containing n units, ...
Implement File Tail and Sensor Health
This interview included two coding tasks. 1. Print the last N lines of a file You are given a very large newline-delimited text file and a limited ...
Implement Fibonacci generator, balanced BST, frozenset
You are coding in Python. Implement the following three tasks. Unless explicitly allowed, do not use Python built-in container types (list, dict, set,...
Stream output until stop token appears
You are implementing a simplified streaming conversational AI output filter. Text arrives in chunks (strings) in order. There is a special stop token ...
Merge overlapping time intervals
Problem: Merge Intervals You are given an array of intervals intervals, where each interval is a pair [start, end] with start <= end. Merge all overla...
Implement common data-structure and JS tasks
You are given several independent coding tasks that appeared across an OA and frontend-focused interviews. Implement each as specified. 1) Time-based ...