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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"Literally just signed a $600k offer. I only had 2 weeks to prep, so I focused entirely on the company-tagged lists here. If you're targeting L5+, don't overthink it."
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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."
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Solve parsing, counting, ranges, and window problems
Solve the following four algorithm problems: 1) Expression evaluator with + and : Given a string s containing non-negative integers, '+' and '' operat...
Compute shortest path between tree nodes
Question You are given the root of a binary tree (not necessarily a BST) whose nodes have integer values, and two target values u and v. Implement a f...
Reverse sublist between equal-value nodes
Given the head of a singly linked list and a target value v that appears at least twice, reverse the sublist starting at the first node with value v a...
Count subarrays summing to target
Given an integer array nums and an integer target T, return the number of contiguous subarrays whose sum equals T. Provide an algorithm that runs in l...
Implement compile-time function type verification
Implement a C++20 compile-time utility to verify whether a callable matches a target function type. Requirements: create a primary template is_callabl...
Maximize reward by scheduling jobs
Given n jobs, each with a start time, end time, and reward, choose a subset of non-overlapping jobs to maximize total reward. Return the maximum rewar...
Return k smallest elements using heap
Given an unsorted array nums of up to 1,000,000 integers and an integer k (1 <= k <= nums.length), return the k smallest elements in ascending order. ...
Maximize one stock trade profit
You're given an array prices of length n where prices[i] is the stock price on day i. You may complete at most one transaction (buy once, then sell la...
Compute reachability and minimal-time same-type scheduling
1) Given four integers a, b, c, d (1 <= a, b, c, d <= 1000), you may perform the following operations any number of times and in any order: (a, b) -> ...
Find root from child adjacency lists
You're given an unordered list describing a rooted n-ary tree. Each item is a record of the form {id: int, children: set<int>} listing a node's direct...
Implement a nested key-value store
Design and implement a nested key–value store that supports set(path, value), get(path), and delete(path), where path is dot-delimited (e.g., "a.b.c")...
Compute intersections for each segment
You are given $n$ segments on a number line. Segment $i$ is the closed interval $[\text{startsAt}[i], \text{endsAt}[i]]$ (inclusive endpoints), with $...
Solve sliding window and tree BFS problems
1) Sliding window: Given an array of positive integers nums and an integer target, return the minimal length of a contiguous subarray whose sum is at ...
Count subarrays with at least k fruit pairs
Given an integer array nums where each value denotes a fruit type, and an integer k: For any subarray, define a 'pair' for fruit value v if its freque...
Implement flat_map and design wealth redistribution
Part 1 — Implement a flat_map: Design and implement an associative container flat_map backed by a sorted dynamic array of (Key, Value) pairs. Support ...
Solve grid path and robot navigation
Part A — Shortest path in a grid with obstacles: Given an m×n grid of 0/1 cells (0 = open, 1 = obstacle), start at (0, 0) and end at (m−1,n− 1). You m...
Implement expression expansion to plus-only form
Given a string expression consisting only of lowercase letters (variables), '+', '*', '(', and ')', return an equivalent expression that uses only '+'...
Implement Luhn-based card validation and inference
Question Implement a set of utilities for credit-card validation and inference using the Luhn checksum algorithm and standard brand patterns. Brand pa...
Calculate trapped water between elevation bars
Given an array of non-negative integers representing the heights of unit-width vertical bars, compute the total water retained after rainfall. Start b...
Implement multi-network card validator with Luhn
Design and implement a payment card validation module that supports multiple networks and error scenarios. Requirements: 1) Luhn checksum - Implement ...