Coding & Algorithms Interview Questions
Practice 3,469 real Coding & Algorithms interview questions for 2026. Covers companies like Meta, Amazon, Google, Uber, and Microsoft. Real questions from actual interviews with detailed solutions — ideal for focused interview preparation. Coding & Algorithms interview questions are the single most common technical gate for software engineering roles and are used to evaluate problem framing, algorithm selection, complexity trade-offs, correctness, edge-case reasoning, and clear communication under time pressure. Expect this category to appear in early technical screens and repeatedly across onsite loops at companies that weight it heavily (notably Meta, Google, and Amazon). Interviews will test arrays and strings, trees and graphs, dynamic programming, hashing and two‑pointer techniques, and the candidate’s ability to test and optimize code in a shared editor. Prepare with timed mock interviews, practice in the same editor you’ll use live, and build a progressive schedule that moves from fundamentals to medium/hard problems; typical candidates invest several weeks to a few months of focused practice depending on seniority and target company.
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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."
"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."
Validate a bracket string
Given a string s containing only the characters '(', ')', '{', '}', '[', and ']', determine whether the input string is valid. A string is valid if: 1...
Solve queue switch and coin change puzzles
This entry contains two separate interview-style quantitative/algorithmic questions. --- 1. Queue switching decision problem You are standing in a sin...
Remove shortest subarray to sort array
Given an integer array nums (length up to 2×10^5), return the shortest subarray [L,R] you can remove so that the remaining elements form a non‑decreas...
Implement streaming autocomplete under tight memory
Build an autocomplete service: Input: a list of up to 5,000,000 UTF-8 words (may include accents and hyphens), each with an integer popularity score t...
Review checkout code for defects and privacy
You are reviewing a supermarket checkout implementation. Identify and prioritize issues and fixes across: (a) monetary correctness (avoid floating poi...
Design airport dispatch with ETA uncertainty
You control airport pickups with streaming ETAs for arriving flights and live driver locations/queues. Design an online dispatch algorithm that minimi...
Implement piecewise linear interpolation for time-to-empty
Time-to-Empty from a Discharge Curve (Piecewise Linear Interpolation) Implement a function time_to_empty(checkpoints, current_soc) that returns the nu...
Implement robust k-means with k-means++ initialization
Implement from scratch in Python (no scikit‑learn) a function kmeans(X, k, max_iter=300, tol=1e-4, random_state=0) that returns (centroids, labels). R...
Design streaming new-vs-returning monthly metrics
Streaming design: Monthly NEW vs RETURNING request shares (event-time, with late/out-of-order and duplicates) Context You receive a high-volume event ...
Design and secure a REST inference API
Design a REST API for Image Inference with Grad-CAM You are designing a public REST API for an image-inference service that accepts large images and r...
Implement K-means and run two iterations
Given points P={(0,0),(0,2),(2,0),(2,2),(8,8),(8,10),(10,8),(10,10)} and k=2, (1) initialize centroids with k-means++ using seed=42 and Euclidean dist...
Maintain a Streaming Median
You are designing a component that receives integers one at a time and must return the current median after each update. Example: - After processing [...
Track Highest-Earning Experience
You are building a core component for a real-time analytics system that tracks the profitability of experiences on a large online platform. Implement ...
Find minimum tanks to cover all houses
You are given a string S representing a street: - 'H' = a house - '-' = an empty plot where you may place a water tank A house is considered covered (...
Find pairs with the minimum absolute difference
Given an integer array (not necessarily sorted), find the minimum absolute difference between any two distinct elements. Return all pairs of values th...
Implement K-means clustering from scratch
This question evaluates competency in clustering algorithms, numerical computation, and practical algorithm implementation, focusing on core K-means c...
Build a least-recently-used cache
This question evaluates a candidate's competence in designing and implementing efficient in-memory cache mechanisms, focusing on data structures, evic...
Maximize Unique Letters
This question evaluates proficiency in combinatorial optimization, bit manipulation, and state-compression techniques for selecting subsets under uniq...
Merge two sorted arrays in-place
This question evaluates array-manipulation and in-place algorithm skills, including understanding of sorted-data merging, index/pointer management, an...
Delete a Character From Cover
This question evaluates proficiency in string manipulation, interval arithmetic, and data-structure updates with attention to index mapping and edge-c...