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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"I honestly don't know how you guys gather so many real interview questions. It's almost scary. I walked into my Amazon loop and recognized 3 out of 4 problems from your database."
"Discovered PracHub 10 days before my interview. By day 5, I stopped being nervous. By interview day, I was actually excited to show what I knew."
"I recently cleared Uber interviews (strong hire in the design round) and all the questions were present in prachub."
"The search is what sold me. I typed in a really niche DP problem I got asked last year and it actually came up, full breakdown and everything. These guys are clearly updating it constantly."
Implement Random Connectivity and Grid Routing
This entry contains two independent coding problems. Problem 1: Uniformly connect node groups You are given k non-empty, disjoint groups of unique nod...
Determine Whether Queries Can Zero Array
You are given an integer array nums of length n and a list of range operations queries, where each query is of the form [l, r, val]. Process the queri...
Move zeros to front
Given an integer array nums, move all 0 values to the beginning of the array in place while preserving the relative order of all non-zero elements. Re...
Compute time to infect all cells
You are given an n × m grid representing people in a city. - Each cell is either infected (1) or healthy (0). - Two cells are neighbors if they share ...
Design a subscription email scheduler with changes and renewals
Implement an email notification scheduler for subscription accounts. Inputs: - send_schedule: a mapping whose keys include: • "start": label to send...
Implement palindrome check and valid parentheses
You have 20–25 minutes per problem. Implement the following two functions and be prepared to explain your approach and time/space complexity. Problem ...
Find Minimum Processing Rate
You are given an array piles, where piles[i] is the number of items in the i-th pile, and an integer h representing the maximum number of hours availa...
Find most frequent call stack from logs
Given an array of log entries for a single-threaded program's function calls, each entry is either '->Name' (function entry) or '<-Name' (function exi...
Find Any Available Meeting Room
You are given multiple meeting rooms. For each room, the existing bookings are represented as a list of non-overlapping time intervals sorted by start...
Find a String Containing Another
Given a list of strings, determine whether any string in the list contains another string from the same list as a contiguous substring. Return one str...
Minimize Operations to Balance Shipments
A shop has n item types, where quantity[i] is the positive integer quantity of the i-th item type. The item types must be shipped in two non-empty con...
Implement Composable Range Iterators
Implement an iterator library: range(start, end, step= 1) supporting forward/backward iteration, inclusive/exclusive endpoints, negative steps, and ov...
Rotate matrix and find max lamp coverage
1) Square-matrix rotation with extra space: Given an n x n integer matrix, return a new matrix that is the 90-degree clockwise rotation of the input. ...
Implement KV store serialization
Implement serialization and deserialization for an in‑memory key‑value store to and from a contiguous bytes buffer. Keys are UTF‑8 strings; values may...
Design receipt system with combo discounts
Question You are building a point-of-sale ordering UI for a food-ordering workflow. You are given class stubs and a callback you must wire up: - Item(...
Design an elevator control system
Design the software for a multi-elevator control system in a high-rise building. Specify classes, scheduling algorithms for car assignments, handling ...
Implement bidirectional Dijkstra for shortest paths
Given a directed or undirected graph with non‑negative edge weights, design and implement bidirectional Dijkstra (“double Dijkstra”) to find the short...
Maximize coins collected by 3-step pieces
You are given a 1D board of length N. Each cell is in one of three states: - Empty - Piece (a movable token) - Coin (collectible) In one move, you may...
Find final URL by crawling until “congrats”
You are given a starting HTTP URL. Implement a function that repeatedly calls URLs returned by previous responses until you reach a response that indi...
Flatten Nested Comments
You are given a list of top-level posts, where each post may contain a list of nested comments, and each comment may itself contain more nested replie...