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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"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."
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Compute root-to-leaf number sum
Given the root of a binary tree where each node stores a digit from 0 to 9, every root-to-leaf path represents a decimal number formed by concatenatin...
Implement K-Means and compare with GMM
Implement K-Means clustering from scratch for a dataset X of shape (n_samples, n_features) and a target number of clusters k. Your implementation shou...
Compute maximum path sum in a binary tree
Question You are given the root of a binary tree where each node contains an integer value (which may be positive, zero, or negative). Return the maxi...
Implement bootstrap mean and variance
You are given an array of N numeric observations x[0..N-1]. Write a function that uses bootstrap resampling to estimate: 1. the mean of the original s...
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 ...
Solve three mini-game algorithm tasks
Solve three mini-game algorithm tasks: (a) Move-House Puzzle: Given initial and target arrangements of N labeled blocks ("houses") on a 2D grid with o...
Compute earliest arrival in time-grid
Question LeetCode 778. Swim in Rising Water – Given an n x n integer grid where grid[i][j] is the earliest time you can enter the cell, starting from ...
Determine reachability and optimize task scheduling
Question LeetCode 780. Reaching Points: Given four integers a, b, c, d (1 <= a, b, c, d <= 1000). Starting from (a, b) you may repeatedly apply either...
How do you escape the circle?
A dog runs continuously along the boundary of a circle of radius 1 at speed 4. You start at an arbitrary point strictly inside the circle and can run ...
Find top-K frequent elements in a stream
You receive a large stream of items (e.g., integers or strings) that may not fit in memory. Design an algorithm that can return the top K most frequen...
Implement an Integer Hash Map
Design a data structure MyHashMap that stores integer keys and integer values without using any built-in hash table library. Implement the following o...
Solve interval deletion and GCD subarray problems
This Amazon online assessment contains two independent algorithm problems. For each, return the requested value, describe an efficient algorithm, and ...
Find top-k lottery winners by spending
You are building a lottery system where each user’s chance of winning is linearly proportional to how much they spent (e.g., user with spend s has wei...
Design a stack with max removal
Design a stack-like data structure for integers that supports the following operations efficiently: - push(x): insert x onto the stack. - pop(): remov...
Maximize weighted subsequence pairs with wildcards
You are given a string s of length n consisting only of characters '0', '1', and '!'. Each '!' can be replaced by either '0' or '1'. For the final bin...
Count Connected Land Regions
You are given an m x n 2D grid representing a map. Each cell is either land ('1') or water ('0'). A land region is formed by connecting adjacent land ...
Simulate robot on grid with obstacles
A robot starts at (0, 0) on an unbounded integer grid. You are given a sequence of commands consisting of characters U, D, L, and R, and a set of bloc...
Compute transaction fees from a CSV string
You are given a CSV string representing a list of payment transactions. Write a function that parses the CSV and returns a CSV string with the total p...
Implement binary search from scratch
Question Implement binary search on a sorted integer array without using any library helpers (no bisect, Arrays.binarySearch, etc.). Provide both iter...
Implement Time-Aware GPU Credit Ledger
Implement an in-memory GPU credit ledger with three operations: - create_grant(amount, start_time, expire_time): add a credit grant. The grant is acti...