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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Solve windowed duplicates and target expression
1) Windowed duplicate check: Given an integer array nums and an integer k, determine whether there exist indices i and j such that nums[i] == nums[j] ...
Implement tree left/right views via BFS and DFS
Given a binary tree, output the left view and right view: for each depth, the first node visible from the left and the first node visible from the rig...
Design two-user communications handler with exceptions
Implement a two-user communications handler. Create: (A) CommsHandler(CommsHandlerABC) with methods connect(self, user1: Caller, user2: Caller) -> str...
Design an efficient Tic-Tac-Toe engine
Design a Tic-Tac-Toe engine on an n x n board. Implement move(row, col, player) -> result where result indicates no winner, player1 wins, player2 wins...
Maximize disjoint k-sum pairs
You are given an integer array nums and an integer k. In one operation you may remove two indices i < j if nums[i] + nums[j] == k; each index can be u...
Maintain top N payers
Implement topNPayers(n) that returns the n accounts with the highest cumulative outgoing payment amounts as strings formatted "{accountId}:{totalOutgo...
Find odd-frequency element with O(1) space
You're given an integer array where exactly one value appears an odd number of times and all other values appear an even number of times. Implement a ...
Implement a GPU credit manager
Implement a GPU credit manager for a compute cluster. Each user has a nonnegative credit balance that can be increased (grantCredits(user, amount)), c...
Find users with access to all cameras
Given entities and relationships (user, owns, camera), (user, belongs_to, group), (group, owns, camera), and (group, belongs_to, group) where groups c...
Explain HashMap internals and collisions
In Java, describe the underlying data structures used by HashMap (e.g., array of buckets, linked lists vs tree bins) and how they evolved across Java ...
Determine reachability and minimum jumps
Given an array of non-negative integers nums of length n, where nums[i] is the maximum number of steps you can move forward from index i: ( 1) Determi...
Design a rolling event tracker with ranges
Design a rolling event tracker that supports time-based queries. Implement a data structure with: ( 1) record(timestamp): record one event at integer ...
Implement factorial and count trailing zeros
Answer the following coding questions in Python. 1) Implement factorial Implement a function factorial(n) that returns \(n!\) for a non-negative integ...
Track simulations and report timeouts
You are implementing a monitoring component for many concurrent simulations. Each simulation produces a stream of event objects of the form: - sim_id ...
Validate complete binary tree
You are given the root of a binary tree. A complete binary tree is defined as a binary tree in which: 1. Every level, except possibly the last, is com...
Design crypto trading order control API
You are implementing part of a simple crypto trading system that manages client orders. Each order can be in one of several states: NEW, ACTIVE, PAUSE...
Compute drawdown, profit, and coin change
Question What is the maximum drawdown of a cumulative PnL (profit and loss) series, and when did it occur? Implement a function mdd(pnl) that returns ...
Compute max-ons and deletion indices
Question Given a circular array of n computers represented by 0 (off) and 1 (on), determine the maximum possible number of on computers within any con...
Solve Open the Lock BFS
Question LeetCode 752. Open the Lock – Given an initial lock state "0000", a target combination, and a list of deadend combinations that cannot be use...
Maximize vacation streak with PTO
Question Given an array of characters containing 'w' (workday) and 'h' (holiday) and an integer n representing the number of PTO days you can convert ...