Coding & Algorithms Interview Questions
Practice 2,960 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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"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."
"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."
Fix a BST with two misplaced keys
You are given the root of a binary search tree in which exactly two nodes’ keys were accidentally swapped. Restore the tree so that its in-order trave...
Solve shortest and label-similar paths
Part A — Unweighted shortest path: You are given an undirected, unweighted graph with vertices labeled 0..n-1 and an edge list. Given start node s and...
Minimize image processing cost with discount
Question You have n images. For the i-th image, processing costs filterCost[i] per day and must run from startDay[i] to endDay[i] inclusive. Each day ...
Solve programming task with follow-ups
Question Pure programming problem solving: implement the core algorithmic solution, then extend it to ( 1) support a constraint of consecutive N eleme...
Convert integer to NAF form
Question Convert a given integer into its Non-Adjacent Form (NAF) representation such that no two non-zero digits are adjacent, and prove that the res...
Count subarrays summing to target
Question LeetCode 560. Subarray Sum Equals K – Given an integer array nums and an integer k, return the total number of continuous subarrays whose sum...
Find LCA in organization tree
Question Given an organizational hierarchy tree, return the lowest common organization (parent node) for two or more employees (≥ 2). Provide unit tes...
Count uniques in sparse sorted array
Question A sorted array contains many duplicates but only a very small number of distinct values. Design an algorithm that counts how many unique numb...
Calculate 95% Bootstrap Confidence Interval for Order Values
Scenario An e-commerce firm wants a 95% confidence interval for the average order value but only has a single historical sample of order amounts. Ques...
Identify Bugs in Python Script for User Assignment
Scenario A simple Python script assigns users to experiment groups and triggers the free-trial offer. Question Inspect the script and list any bugs or...
Design a Scalable, Fault-Tolerant Distributed Order System
Scenario Round covering distributed-system design and algorithm implementation. Question Design a highly available, low-latency distributed order-proc...
Identify Number Pairs Adding to Target in Array
Scenario Coding round to identify all number pairs that add up to a target in an array containing duplicates. Question Given an integer array (may con...
Sort and Rearrange: Efficient Algorithms for Diverse Challenges
Scenario Coding rounds and infrastructure-style algorithm questions. Question Write an efficient algorithm to return the length of the longest increas...
Identify Pirate-Themed Custom Themes Using Jaccard Similarity
Scenario Engineering receives two lists and must identify custom themes that look like Pirate themes. Question a) Write a Python function that compute...
Compute sliding window sums by tag
Question Given a list of datapoints where each datapoint has tags, a timestamp, and a value, write a function that, for a specified tag t and window s...
Solve vertical order & diameter variants
Question LeetCode 314. Binary Tree Vertical Order Traversal LeetCode 543. Diameter of Binary Tree – modified to return the number of nodes (edges + 1)...
Parse strings and find meeting slots
Question Given a text file where each line contains raw information, extract the user identifier and the numeric quantity on that line and store the r...
Find names similar by one swap
Question LeetCode 859. Buddy Strings – Given a target string and a list of strings, return all list entries that can match the target by swapping at m...
Implement tree ops and LRU cache
Question Implement set(index) and clear(index) for the leaves of a full binary tree initially filled with 0s, where a parent node becomes 1 only when ...
Solve diameter and shortest bridge problems
Question LeetCode 543. Diameter of Binary Tree LeetCode 934. Shortest Bridge https://leetcode.com/problems/diameter-of-binary-tree/description/ https:...