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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Find longest common contiguous subarray
Given two integer arrays A and B, find the length of the longest contiguous subarray that appears in both arrays. If multiple exist, return any one pa...
Design a single-machine LRU cache
Design an in-memory LRU cache for a single machine using a hash map and a doubly linked list to support O( 1) get and put. Explain how you handle capa...
Design a coupon pricing engine
Design and implement a coupon application engine for a shopping cart. Each Item has id, category, and unitPrice. A Coupon has: applicableCategories (o...
Design an in-memory database with TTL and history
Design and implement an in-memory key–field–value store with monotonic timestamps. Keys and fields are strings; values are integers. Provide these API...
Implement KV store and plan type conversions
Part 1 — Versioned key-value store: Implement a data structure with set(key, value, t) and get_at(key, t) that returns the value for key whose timesta...
Find kth smallest in sorted matrix
Given an n x n matrix where each row and each column is sorted in nondecreasing order, and an integer k (1 ≤ k ≤ n^ 2), return the k-th smallest eleme...
Compute binary tree left-side view
Given a binary tree, return the values visible from the left side when looking from top to bottom. If multiple nodes exist at the same depth, the left...
Verify permutation in-place and implement fast power
1) Given an integer list A of length n, determine whether A is a permutation of [0, 1, ..., n-1]. Do it in-place with O( 1) extra space (no auxiliary ...
Count non-decreasing arrays by digit sums
You are given an array required_sums of length n. Count how many non-decreasing arrays result[1..n] of integers satisfy all of the following: ( 1) for...
Design a fixed-capacity circular queue
Design a fixed-capacity circular queue that supports enqueue(x), dequeue(), front(), rear(), isEmpty(), and isFull() operations in O( 1) time. Impleme...
Implement drawdown, single-trade profit, coin change
Implement and analyze the following three problems: 1) Maximum drawdown of cumulative PnL: "What is the maximum drawdown of a cumulative PnL (profit a...
Solve sliding window and tree BFS problems
1) Sliding window: Given an array of positive integers nums and an integer target, return the minimal length of a contiguous subarray whose sum is at ...
Compute reachability and minimal-time same-type scheduling
1) Given four integers a, b, c, d (1 <= a, b, c, d <= 1000), you may perform the following operations any number of times and in any order: (a, b) -> ...
Solve minimum rate and subset sum
1) Minimum rate to finish vaults within a deadline: You are given an array vaults of positive integers representing the amount in each vault along a r...
Solve array modulo and parentheses tasks
Implement two tasks: 1) Count subarrays by modulo remainder - Input: integer array nums (length n), integers K (1 ≤ K ≤ 10^ 4) and R (0 ≤ R < K). - Ou...
Solve parsing, counting, ranges, and window problems
Solve the following four algorithm problems: 1) Expression evaluator with + and : Given a string s containing non-negative integers, '+' and '' operat...
Implement valid 1-D convolution with bias
Question Implement a "valid" 1-D convolution function in the cross-correlation sense. Given an input array of numbers, a kernel (filter) array of numb...
Compute longest increasing subsequence
Longest Increasing Subsequence: length, reconstruction, and counting Given an integer array nums, do all of the following: 1. Length. Compute the leng...
Compute islands in a binary grid
You are given an m-by-n grid of characters where '1' represents land and '0' represents water. Count the number of connected land masses (islands) usi...
Implement BST vertical traversal and list conversion
Given the root of a binary search tree (BST): 1) Implement vertical order traversal: assign the root column 0, left child column −1, right child colum...