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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Implement Kac ring with O(1) color and kstep
You are implementing a Kac ring dynamical system. Model - There are N positions arranged in a circle, indexed clockwise: 0, 1, ..., N-1. - Each positi...
Count distinct palindromic subsequences
Given a string s consisting of lowercase English letters, compute how many distinct palindromic subsequence strings of lengths 2, 3, and 4 can be form...
Find Final Ball Holder
This question evaluates understanding of functional graphs, cycle detection, and handling large-step transitions in deterministic mappings where repea...
Reverse nodes in even-length linked-list groups
Problem Given the head of a singly linked list, you will traverse the list in contiguous groups of increasing size: the 1st group has size 1, the 2nd ...
Find maximum follow depth using recursion
You are given a directed follows relationship representing a social graph: - Each record (follower_id, followee_id) means follower_id follows followee...
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 ...
Compute length of longest increasing subsequence
You are given an integer array nums of length n. A subsequence of nums is a sequence that can be derived from nums by deleting zero or more elements w...
Maximize Unique Characters from Words
You are given a list of lowercase English words. Select a subset of the words such that no character appears more than once across all selected words....
Solve string and hashmap interview tasks
Coding questions (solve both) 1) First non-repeating character Given a string s, return the first character that appears exactly once in the string. -...
Find kth largest element in array
Question Given an unsorted array of integers nums and an integer k, return the k-th largest element in the array. The 1st largest element is the maxim...
Generate all safe queen placements on board
You are given an integer n representing the size of a chessboard (n × n). You need to place n queens on the board so that no two queens attack each ot...
Merge overlapping intervals
You are given a list of closed intervals on the number line, where each interval is represented as a pair of integers [start, end] with start <= end. ...
Compute cart total with best promotion
Assume you are implementing a checkout price calculator for an online shopping cart. You are given: - A list of items in the cart. Each item has: - ...
Design crypto trading order control API
You are implementing part of a simple crypto trading system that manages client orders. Each order can be in one of several states: NEW, ACTIVE, PAUSE...
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...
Design body camera checkout system
This question evaluates competency in in-memory data structure design, algorithmic complexity (achieving O(1) average operations), and randomized reso...
Determine Straight Flush
This question evaluates competency in algorithmic pattern detection and data-structure manipulation applied to domain-specific representations, focusi...
Find largest group of two-digit numbers sharing digits
You are given an integer array A of length n (1 <= n <= 100). Each element is a two-digit number (e.g., from 10 to 99). Two numbers are considered con...
Count Same-Day Registered Posters
You are given two tables: `text users - user_id: unique identifier for a user - registered_at: timestamp when the user registered posts - post_id: uni...
Simulate Threshold Grid Infection
This question evaluates understanding of discrete grid-based simulations and local state-transition rules, focusing on modeling infection spread, neig...