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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Sort characters by frequency
Given an ASCII string s, reorder its characters in decreasing order of frequency. If multiple characters share the same frequency, break ties by ascen...
Maximize profit with transaction fees
You are given an array prices where prices[i] is the price of a stock on day i and an integer fee representing the commission charged when you sell. Y...
Design file deduplication at scale
Design an algorithm to identify duplicate files in a large directory tree. You are given an iterator over files providing (path, size) and a function ...
Simulate fixed-shape tiling on a grid
You are given an empty n-by-m grid and a list of tile patterns, patterns[0..k-1]. Each pattern is a binary matrix (1 = filled cell, 0 = hole) and must...
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 horizontal cut balancing square areas
Given a 2D table with top-left origin (0, 0), you are provided a finite set of n non-overlapping, axis-aligned square cakes. Each square i has real-va...
Implement a sliding-window hit counter
Implement a hit counter that supports recordHit(timestamp) and getHits(pastSeconds). Use a fixed-size array to maintain a sliding time window (e.g., l...
Implement prefix and suffix file search
Implement data structures and APIs to store file names and support efficient queries that match both a given prefix and suffix. Provide methods add(na...
Detect runs and collapse a numeric grid
You are given an m x n grid of digits (0– 9). Phase 1: Find every horizontal or vertical run of length ≥ 3 consisting of the same digit. For each run,...
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...
Design LCA and find K closest points
Part A — LCA with parent pointers: You are given two nodes a and b in a rooted tree where each node has a parent pointer (you may or may not have dire...
Implement hostname-restricted web crawler
Implement a single-threaded web crawler that, given a starting URL startUrl and an interface getUrls(url) that returns all hyperlinks on the page at u...
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...
Convert stack samples to execution trace
You are given sampling-profiler output: a list of Sample objects ordered by timestamp ascending. Each Sample has (t: float, stack: list[str]) where st...
Design a nested-list iterator
You are given a nested structure that can contain integers or further lists. Design an iterator over this structure that returns integers in left-to-r...
Compute exclusive times and call stack from logs
Design an algorithm that, given a single-threaded program's execution log, computes per-function exclusive durations and reconstructs the active call ...
Find next and closest palindromes
Given a non-negative integer represented as a string n (no leading zeros unless n == "0"), return the smallest palindromic integer strictly greater th...
Find max-score path in weighted DAG
You are given a directed acyclic graph (DAG). Each node v has a score w(v). Each directed edge (u→v) has a nonnegative time cost t(u,v). There is a un...
Implement 2D word search variants and analyze complexity
Given an m x n grid of uppercase letters board and a string word, implement two related functions: ( 1) Fixed-direction search: Return true if word ap...
Find earliest common meeting slot
Question Given the calendars of N attendees, find the earliest time window of length at least d minutes during which all attendees are simultaneously ...