Coding & Algorithms Interview Questions
Practice 2,960 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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Implement Billing Coding Exercises
You are interviewing for a software engineering role at a payments company. The coding rounds focused on practical billing workflows. Implement the fo...
Implement templated string replacement
You are given: 1. A dictionary (map) of placeholder keys to values, for example: `python values = { "db_host": "example.com", "db_port": 5001 } ` ...
Build an Expense Policy Rule Engine
Implement a simplified expense-policy rule engine. An expense record contains: - amount: number - category: string - merchant: string - country: strin...
Implement LRU, Extend to LFU, Analyze Complexity
Implement an in-memory Least Recently Used (LRU) cache with capacity N that supports get(key) -> value and put(key, value). Achieve O( 1) average time...
Design error detection and propagation algorithms
You are given three related sub-problems about error detection and propagation. A) Log search: You have a chronologically ordered array of log lines. ...
Determine and print expression to reach target
You are given four numbers and a target T (e.g., 24). Using +, −, ×, ÷ and parentheses, and using each number exactly once, determine whether you can ...
Find normalized list difference efficiently
Given two lists of strings, list1 and list2, return all elements that appear in list1 but not in list2 after applying a consistent normalization step ...
Design an O(1) eviction cache
Implement an in-memory key–value cache with fixed capacity that evicts the least recently used entry when full. Support get(key) -> value or -1 if mis...
Implement write with internal buffer
Implement a buffered writer over an expensive sink API. You are given a function writeToDevice(byte[] chunk) that may accept at most M bytes per call ...
Design Manhattan-distance meeting point finder
Given an m×n grid with cells marked 1 for homes and 0 otherwise, choose a single meeting cell that minimizes the sum of Manhattan distances from all h...
Merge two sorted arrays in-place
You are given two nondecreasing arrays A and B, where A has enough trailing empty slots to hold all elements of B. Merge B into A in-place so that A r...
Implement string dedup and mirror tree traversal
- String cleanup with group deletions (LeetCode-inspired): Given a string s consisting of lowercase letters, repeatedly delete any maximal contiguous ...
Determine frog reachability across stones
You are given a sorted array of distinct integers stones representing stone positions in a river, where stones[0] = 0. A frog starts on stone 0; its f...
Find top co-purchased products
You receive purchase logs where each order is represented as an integer array of product IDs bought together in a single transaction. Implement a func...
Maximize ones with limited flips
Given a binary array and an integer k, return the length of the longest contiguous subarray achievable by flipping at most k zeros to ones. Explain an...
Find earliest time password becomes irrecoverable
You are given a password string of length n and an attack order array attackOrder[1..n], a permutation of 1..n. At second i (1-indexed), the virus rep...
Detect intersection of two linked lists
Given two singly linked lists that may converge to share a common tail, determine whether they intersect and return the first node at which they join....
Debug a driver assignment bug
Given a service that selects the best delivery driver ("dasher") for an order, users report incorrect assignments. With a provided codebase and failin...
Solve matrix components, median, and traversals
1) Binary matrix component: Given an m x n grid of 0s (background) and 1s (objects), return the size of the largest connected component where connecti...
Solve Grid and Counting Problems
A software engineering intern phone screen included two coding tasks: 1. Count islands in a grid Given an m x n grid of characters where '1' re...