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."
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Return right and left side views of a tree
Given the root of a binary tree, compute two “side views”: 1. right_view: the list of node values visible when looking at the tree from the right side...
Merge multiple sorted arrays using min-heap
Problem You are given k sorted arrays of integers: - arrays[0], arrays[1], ..., arrays[k-1] - Each arrays[i] is sorted in non-decreasing order. - The ...
Solve Three Algorithmic Problems
Three coding questions were mentioned: 1. Second-largest distinct permutation Given an array of integers that may contain duplicates, consider all ...
Implement three whiteboard coding tasks
The interview report described several coding questions in the same category: 1. Binary search: Given a sorted array of integers and a target value, r...
Compute rolling standard deviation in O(n)
Given an array of numbers and a window size k, compute the rolling standard deviation for every contiguous window. Design an O(n) algorithm that updat...
Maximize area between vertical lines
Problem You are given an integer array h where h[i] represents the height of a vertical line drawn at x-coordinate i. Choose two different indices i <...
Design LFU cache with distributed extension
Problem You are asked to design and implement a data structure that behaves like an in-memory cache with a Least Frequently Used (LFU) eviction policy...
Compute nearest courier for each customer
Question You are given two sets of 2D points: customers C = {c1..cn} and active couriers (dashers) D = {d1..dm}. Each customer i has coordinates (xi, ...
Implement 3x3 matrix transforms and rotation
For a 3x3 matrix, write Python code to: (a) transpose it in-place; (b) swap any two rows and any two columns; (c) reverse a specified column and rever...
Compute Sliding Window Averages
Given a list of numbers nums and a positive integer window_size, compute the average of every contiguous subarray of length window_size. Return a list...
Count Enclosed Islands in a Grid
You are given an m x n grid representing land and water after flooding. - 0 represents land. - 1 represents water. - Two land cells belong to the same...
Apply sliding window techniques
Explain the sliding window technique and apply it to solve: ( 1) Given an array of positive integers and a target S, return the minimal length of a co...
Implement two array-cost minimization algorithms
Implement two array-cost minimization algorithms that appeared back-to-back in an AWS SDE online assessment. Each can be solved independently. Part 1 ...
Parse and expand an IPv6 address
Implement an IPv6 address parser/normalizer. You are given a string s that may represent an IPv6 address using standard notation: - Up to 8 groups (“h...
Implement most_frequent_key without using max()
Problem (Python OOP) You are given two classes. Parent precomputes frequency counts of items (as strings) from an input list. `python class Parent: ...
Compute maximum non-overlapping meetings
Assume you are given a list of meeting time intervals for a single person. Each meeting i is represented by a pair of integers [start_i, end_i], where...
Shuffle array using random integer API
You are given an array nums of length n representing a deck of distinct cards. You do not have access to a built-in shuffle function, but you are give...
Find user pairs with overlapping last K movies
You are given the same user movie-watching histories as in the previous problem. Each user’s history is an ordered list of movie IDs from earliest to ...
Explain differences between Python list and tuple
In Python, what are the key differences between a list and a tuple? Cover: - Mutability and implications - Performance and memory considerations (high...
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...