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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Design a bank with scheduled payments and merges
Design an in-memory banking service that supports the following operations: ( 1) CreateAccount(accountId), ( 2) Deposit(accountId, amount), ( 3) Trans...
Populate next pointers in a perfect binary tree
You are given a perfect binary tree (all leaves at the same level; every internal node has two children). Each node has fields left, right, and next. ...
Solve maze reachability and two follow-ups
You are given three independent coding tasks. 1) Maze reachability with “rolling ball” movement Given an m x n grid maze where 0 means empty and 1 mea...
Implement Election Report and Banking Pipeline
You are given two independent data engineering coding tasks. Task 1: SQL Election Exit Poll by State Report An election analytics team needs a report ...
Design a snapshotable key-value store
Design and implement a snapshotable key–value map supporting the following APIs: - S(key, value): set the current value of a string key to a string va...
Implement string reduction and time map
In a coding interview, you are asked to solve two algorithm problems. 1. String reduction with adjacent duplicates - Basic version: Given a string ...
Find next greater element for subset
You are given two integer arrays query and nums. - All elements in nums are distinct. - Every element in query also appears in nums. For each value x ...
Count closed islands in a grid
Problem You are given an m x n 2D grid representing a map after flooding: - 0 = water - 1 = land An island is a maximal 4-directionally connected comp...
Solve two online assessment problems
An online assessment contained two coding problems: 1. Maximize skipped positions You are given an array of length n indexed from 0 to n - 1. Start...
Implement BST Iterator and Ticket Queue
The coding interviews mentioned two algorithm/data-structure tasks: 1. Implement a binary search tree iterator. You are given the root of a binar...
Solve pair-counting and account-merging problems
Problem A — Count qualifying products You are given two integer arrays A and B, and an integer T. For each element a in A, count how many elements b i...
Find Top K Largest Elements
Given an unsorted integer array nums of length N and an integer k such that 1 <= k <= N, return the k largest elements in the array. If a value appear...
Sample index from weighted probability distribution
Given an array weights[0..M-1] representing a discrete distribution over M outcomes, implement a function sampleIndex(weights) that returns an index i...
Solve two interval array problems
You are given two interval-based tasks from a technical screen for a data engineering role. 1. Merge overlapping intervals - Input: an array of int...
Sample uniformly from a circle’s area
How would you generate a point (x, y) uniformly at random from the area of a circle of radius R centered at the origin? - Explain why naive choices (e...
Solve k-Nearest Places by Latitude/Longitude
Given a set of geographic coordinates and a query point, return the k nearest locations. Describe how you compute great-circle distance (e.g., Haversi...
Implement Sliding Windows and LRU Cache
You are given two coding tasks. Task 1: Longest Subarray of Ones Given a binary array nums and an integer k, return the maximum length of a contiguous...
Design compressed vector and compute dot product
Problem You are given very long integer vectors where many adjacent elements repeat (e.g., long runs of the same value). Storing the full array is mem...
Solve path and inventory problems
The coding rounds contained two algorithmic exercises: 1. Maximum multiplier path You are given an m x n grid of integers. Start at the top-left ce...
Find Largest Adjacent Stock Price Change
You are given an unsorted list of stock price records. Each record has two fields: - date: a date string in YYYY-MM-DD format - price: an integer stoc...