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."
"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."
Design a time-windowed key-value store
Implement a time-windowed key-value store ("Windowed Map") that receives key/value updates at irregular times and only keeps entries from the most rec...
Calculate Per-User Usage Charges
Implement a billing function for an AI text API. You are given usage records for a single billing cycle. Each record contains: - user_id - input_token...
Solve Three OA Coding Tasks
This online assessment included the following coding problems: 1. Reverse the middle of vowel-bounded words You are given an array of lowercase str...
Check palindrome and find next larger palindrome
Problem: Palindrome Check + Next Larger Palindrome Part 1: Palindrome validation Given a string s, determine whether s is a palindrome (reads the same...
Identify the Extra Directed Edge
You are given a list of directed edges edges, where each edge is represented as [parent, child]. The graph contains nodes labeled from 1 to n, and it ...
Find max distance between alive tree nodes
Given a binary tree, define alive nodes. Base case: alive nodes are the leaves. Find the maximum distance (number of edges) between any two alive node...
Solve three coding interview problems
You are given three independent coding questions. 1) Decode an encoded string Given an encoded string s, decode it using the following rule: - Pattern...
Implement and use a version comparator
You are given up to 100,000 version-like identifiers (e.g., "1.0", "01.2.0", "2.0.0-alpha", "1.10.3"). Implement compare(a, b) that orders identifiers...
Simulate Threshold Grid Infection
You are given an m x n binary grid where 1 means infected and 0 means healthy, along with an integer K. The system evolves in discrete time steps. Dur...
Implement Concurrent Utilities in C++
Implement two related C++ concurrency tasks. 1. Templated parallel execution utility: Write a generic function or class template that accepts a slow c...
Implement a dictionary without built-in Dictionary
Implement a key-value map type (a “dictionary” / hash map) from scratch, without using the language’s built-in dictionary/map as the underlying storag...
Schedule vector ops on heterogeneous cores
You are optimizing a “vectored computation” on a heterogeneous (non-SMP) CPU with asymmetric cores. Hardware model There are two core types: - D-cores...
Implement a size-bounded LRU cache
Design and implement an LRU (Least Recently Used) cache where the cache capacity is measured by total size, not by item count. Each cached item has a ...
Compute minimum semesters to finish courses
You are given n courses labeled 1..n and a list of prerequisite relations prereq, where each element is a pair [a, b] meaning you must complete course...
Find shortest subarray meeting target sum
Given an integer array nums (values may be negative) and an integer T, return the length of the shortest non-empty contiguous subarray whose sum is at...
Validate a training courses catalog
You are given a catalog of training courses. Each course has: - a unique course_id - a list of prerequisite course IDs prereqs (possibly empty) Write ...
Determine a one-step string transformation
Given two lowercase strings source and target, determine whether target can be obtained from source using at most one of the following operations, and...
Build next-word predictor with O(1) lookup
Problem You are given a training corpus where each training example is a tokenized sentence (array of words). Example training sentences: - ["I", "am"...
Maximize weighted sum with disjoint adjacent swaps
You are given an integer array arr of length n (0-indexed). Define the weighted sum as: S = Σ_{i=0..n-1} arr[i] * (i + 1). You may perform any number ...
Find K-th Largest and Longest Vacation
Solve the following two coding problems. 1. Find the k-th largest element Given an integer array nums and an integer k, return the element that wou...