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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Solve various LeetCode data-structure questions
Question LeetCode 129. Sum Root to Leaf Numbers LeetCode 2089. Find Target Indices After Sorting Array LeetCode 270. Closest Binary Search Tree Value ...
Allocate refund across payments
Question Given a list of completed payment transactions (each with payment method, date, and amount) and a refund amount R, write an algorithm that is...
Compute minimum passes to collect numbers
Question You are given an array shelf of n distinct integers that is a permutation of 1…n. Starting with target = 1, you repeatedly scan shelf from le...
Count deletions making array fair
Question LeetCode 1664. Ways to Make a Fair Array – Given an integer array nums, count the indices whose removal results in the sum of elements at eve...
Solve array and list algorithms
Question LeetCode 315. Count of Smaller Numbers After Self LeetCode 23. Merge k Sorted Lists Design algorithm for Amazon Locker getPackage (retrieve p...
Explain strings, moves, and concurrency
Question What is a string in programming languages? What fields are stored in a typical struct string and how would you implement one yourself? What i...
Compute maximum distinct-product pickup days
Question Given an array of positive integers representing quantities of different products, on day i (starting from 1) you must pick exactly i distinc...
Calculate area, flush probability, egg drops
Question Given two quarter-circles inside a 1×1 square (centers at bottom-left and top-right corners), find the exact area of their overlapping region...
Solve island connectivity and string multiplication
Question Given N distinct islands (e.g., a, b, c…) and a list of existing undirected paths between them, compute the minimum number of additional path...
Count islands and distinct shapes
Question LeetCode 200. Number of Islands LeetCode 694. Number of Distinct Islands https://leetcode.com/problems/number-of-islands/description/ https:/...
Design timestamped key-value map
Question Design a class that supports insert(key, value, timestamp) and get(key, timestamp) where get returns the value whose timestamp is the smalles...
Design prefix-sum function and max stack
Question LeetCode 303. Range Sum Query – Immutable (design a reusable prefix-sum function) LeetCode 716. Max Stack (similar design question) https://l...
Navigate maze via HTTP API
Question Implement a program that repeatedly calls a provided HTTP API which returns the next URL in a maze; continue following the URLs until reachin...
Compute product of array except self
Given an integer array nums, return an array out where out[i] equals the product of all elements in nums except nums[i]. Do it in O(n) time using cons...
Traverse levels selecting nodes meeting a predicate
Given the root of a binary tree and a predicate P(value) that returns true for certain node values, return a list of lists where the i-th list contain...
Find minimum and most frequent number efficiently
Given an unsorted integer array, write functions to: (a) find the minimum value; and (b) find any value that occurs most frequently (if multiple value...
Design a constrained in-memory file system
Design an in-memory hierarchical file system. Implement: 1) addFile(String path): Given a UNIX-style absolute path like "/path/to/somewhere/file.txt",...
Solve prefix, array, and string problems
The interview included several coding problems: 1. First index matching a prefix: Given a sorted array of lowercase strings such as ["a", "apple", "ap...
Find and remove duplicate files
Given a directory tree that may not fit in memory, detect and optionally remove duplicate files. Define the algorithm, including how you handle very l...
Find latency pairs with minimal difference
Given an array of integers representing network latencies, return all increasing pairs [a, b] such that b − a equals the minimal absolute difference b...