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."
Maximize profitable pairs
You are given an array profits of n integers representing net profit per item and an integer threshold T. You may form disjoint pairs (i, j). What is ...
Compute top-K branches by openings
Given a stream of account-opening events (branch_id, user_id, timestamp), design algorithms and data structures to compute the top-K branches by numbe...
Implement firewall matching with CIDR rules
Implement a simple IPv4 firewall rule matcher. Problem You are given an ordered list of firewall rules. Each rule has: - an action: ALLOW or DENY - a ...
Compare final, finally, finalize
Compare Java's final keyword, the finally block, and the finalize() method. For each, explain purpose, typical use cases, lifecycle/semantics, and com...
Sort a string by custom order
Given a priority string P of distinct characters and a text string S, reorder S so that all characters appearing in P come first and are grouped in th...
Compute binary tree diameter
Given the root of a binary tree, compute the tree's diameter defined as the maximum number of edges on any path between two nodes. Return the diameter...
Design LCA with flexible inputs and rule
Design a function to find the lowest common manager of two employees in an organizational tree. Support two input models: (A) nodes store a list of ch...
Assess HashMap vs ConcurrentHashMap
Is Java's HashMap thread-safe? Explain why or why not. How does ConcurrentHashMap achieve thread safety and performance (e.g., lock striping, CAS oper...
Implement substring search and weighted sampling
Two coding questions were asked in the onsite. 1. Substring search: Given two strings text and pattern, return the starting index of the first occurre...
Implement a String Deque
Implement a double-ended queue (Deque) that stores strings. Your implementation must support the following operations: - addFirst(data): Insert data a...
Implement PyTorch training loop
Implement a basic PyTorch training loop You are given a PyTorch neural network model, a DataLoader that yields (inputs, targets) batches, an optimizer...
Compute median of two sorted arrays
You are given two sorted arrays of integers nums1 and nums2. - nums1 has length m, nums2 has length n. - Both arrays are sorted in non-decreasing orde...

Find LCA in a N-ary tree via DFS
You are given the root of a rooted N-ary tree (each node can have zero or more children) and two distinct nodes p and q that belong to the tree. Desig...
Find shortest jumps in circular array
You are given a circular array arr of length n. From index i, you may jump exactly arr[i] steps either to the left or to the right (wrapping around th...
Implement Distributed Matrix Multiplication
You are given a simplified distributed-computing setup that simulates communication between devices using Python threads and message queues. A helper ...
Solve Two Grid Search Problems
Solve the following two coding problems. 1. Count disconnected land regions - You are given an m x n grid of characters where '1' represents land a...
Fetch, group, and print paginated activities
Question Given a paginated API that returns (totalCount, activities[]) for a requested page, implement code that iterates through all pages and prints...
Compute statistics in data stream
Question Design a data structure that supports computing the current max, mean, and mode for an unbounded integer data stream. Estimate the memory usa...
Verify and modify inorder subsequence
Question Given a binary tree and a sequence of numbers, design an algorithm to check in O(n) time and O( 1) extra space whether the sequence is a subs...
Implement flat_map, redistribute wealth evenly
Question Implement std::flat_map in C++, including its iterator; explain design choices and add thorough test cases. Given an array of integers repres...