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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Count user sessions from logs
Given a large log file where each line is "timestamp,user,action", compute the number of sessions per user. Assume a session ends if the gap between c...
Maximize ones with limited flips
Given a binary array and an integer k, return the length of the longest contiguous subarray achievable by flipping at most k zeros to ones. Explain an...
Search a word in a grid
Given a 2D grid of characters and a target word, determine if the word can be traced by moving up, down, left, or right, using each cell at most once....
Solve load balancing and perfect pairs
1) Contiguous load balancing: You have n identical resources (servers) and m ordered tasks with processing times burstTime[0..m-1]. Each server must b...
Implement LRU, Extend to LFU, Analyze Complexity
Implement an in-memory Least Recently Used (LRU) cache with capacity N that supports get(key) -> value and put(key, value). Achieve O( 1) average time...
Compute grid shortest path with obstacles
You are given an m x n grid of integers where cells with value -1 represent obstacles and all other cells are traversable. Starting at (0, 0) and targ...
Detect cycles in lists and graphs
Given a singly linked list, determine whether it contains a cycle. Implement an O( 1)-space algorithm and explain the intuition and correctness. Follo...
Solve six algorithmic problems
Answer the following independent algorithmic prompts. For each, explain your approach, justify data structures, analyze time/space complexity, and pro...
Solve jumps and anagram-similarity problems
You are given two independent tasks. Task A (Maximize calories over jumps): - There are n blocks with integer heights height[i] ≥ 0. - You start on th...
Implement automatic braking logic in Python
Using Python, implement a simple automatic braking function. Given current speed v (m/s), distance to obstacle d (m), maximum deceleration a_max (m/s^...
Count subarrays with product under target
Given an array of positive integers nums and an integer T > 1, return the number of contiguous subarrays whose product is strictly less than T. Provid...
Implement BFS serializer and deserializer
Implement two functions, serialize(obj) -> representation and deserialize(representation) -> obj, for a Python object graph containing str, int, and d...
Maximize credits with limited skips
You are given n warehouses with inventories inventory[0..n-1], and two dispatch amounts: you dispatch dispatch1 units first each turn, then your co-wo...
Design error detection and propagation algorithms
You are given three related sub-problems about error detection and propagation. A) Log search: You have a chronologically ordered array of log lines. ...
Mirror a binary tree and analyze complexity
Given the root of a binary tree, convert it to its mirror by swapping every node’s left and right children. Implement both recursive and iterative (us...
Find normalized list difference efficiently
Given two lists of strings, list1 and list2, return all elements that appear in list1 but not in list2 after applying a consistent normalization step ...
Compute top-N active customers
Maintain and return the top N customers by cumulative activity amount, where activity is defined as the sum of deposit amounts, pay amounts, and trans...
Fill rooms with nearest gate distances
You are given an m×n integer grid representing rooms, where -1 is a wall, 0 is a gate, and INF (a large sentinel such as 2^31− 1) is an empty room. Fo...
Compute min operations to transform integers
Given integers A and B, transform A into B using the minimum number of operations. Allowed operations: ( 1) subtract 1 from the current value; ( 2) mu...
Solve a Skyscraper puzzle efficiently
Design and implement a solver for the Skyscraper logic puzzle on an $N \times N$ grid, where $3 \le N \le 7$. The board is a grid of building heights....