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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Maximize protected population with one-step guard shifts
There are n cities in a line (1-indexed). You are given: - population[1..n]: population of each city - unit: a binary string of length n, where unit[i...
Implement Streaming Word Counter
Implement a class that records word frequencies from a stream of text. The class should support the following operations: 1. add_text(text: str) -> No...
Solve PTO window and sparse unique counting
Design algorithms for two problems: A) Longest vacation with limited PTO: Given an array A of characters where 'w' denotes a workday and 'h' denotes a...
Parse a password from a matrix
Given an m x n matrix of characters, a starting coordinate (row, col), and a string of moves consisting of 'U', 'D', 'L', 'R', parse a password by vis...
Find Affected Services After Shutdown
You are given a set of services and their dependency relationships. The input is a hash map where each key is a service name, and the value is a list ...
Find and count target-sum subarrays
Given an integer array nums and an integer target, implement: ( 1) a function that returns true if any non-empty contiguous subarray sums to target; (...
Implement island counting with BFS and DFS
Question You are given an m x n grid of characters where '1' represents land and '0' represents water. Count the number of distinct islands (connected...
Find lowest common ancestor in tree
You are given the root of a binary search tree (BST) and two distinct nodes p and q that are guaranteed to exist in the tree. Task (BST case): - Find ...
Can the character reach the destination?
You control a character starting at a start cell and want to reach a target cell in a 2D grid. Some cells are blocked by obstacles and cannot be enter...
Compute widest level span in a binary tree
Given a binary tree, define the width of a level as the number of positions between the leftmost and rightmost non-empty nodes at that depth when node...
Implement four DS coding tasks
You are completing a CodeSignal-style assessment (Python or R). Implement solutions for the following four independent questions. 1) Two-sample z-test...
Build a Tic-Tac-Toe App
Implement a simple Tic-Tac-Toe mobile app that can be completed in a 45-minute coding interview. Requirements: - Display a 3x3 board. - Support two lo...
Maximize stock profit with one or two trades
You are given an array prices where prices[i] is the price of a given stock on day i (0-indexed). You want to maximize your profit by choosing when to...
Solve constrained monster traversal
You are given a directed graph with n rooms labeled 0..n-1; each room i contains a monster with health hp[i] ≥ 0. You start at room s with energy E. E...
Solve tree, array, and maze tasks
You are given a set of algorithmic problems from a software engineering onsite. 1. Tree path length: Given the root of a binary tree, return the numbe...
Solve several coding interview problems
The interview included the following coding problems: 1. Decode ambiguous Morse text: Use the standard Morse mapping for letters A-Z. You are given a ...
Construct a BST and read spiral order
The coding round reportedly included two algorithmic tasks: 1. Rebuild a binary search tree from a preorder sequence - You are given an array of di...
Find duplicate files and apply image operations
Part A — Find duplicate files by content You are given a list of directory records. Each record is a string describing a directory path followed by on...
Compute unique-substring length and first unique index
Solve the following two string problems. Problem 1 — Longest substring with all distinct characters Given a string s, find the length of the longest c...
Maximize sum with no adjacent tree nodes
Given the root of a binary tree where each node contains an integer value (can be 0 or positive), choose a subset of nodes such that no selected node ...