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."
Implement an LRU cache
Design and implement a data structure for a Least Recently Used (LRU) cache with a fixed capacity. The cache must support: - get(key): return the valu...
Evaluate arithmetic expression with variables
Implement an expression evaluator for a string expr containing non-negative integers, variables (alphabetic names), operators +, -, , /, parentheses '...
Implement a key-value CRUD store
Implement an in-memory key–value store that supports create, read, update, and delete operations. Expose APIs such as put(key, value), get(key), updat...
Implement anagram check and odd-even linked list
You are given two independent coding tasks. Task 1: Check if two strings are anagrams Implement a function that determines whether two given strings a...
Implement staircase printing and distributed mode/median
Problem A: Print a “staircase” pattern Implement a function that prints a staircase with n rows. Input - An integer n (n >= 1) Output - Print n lines....
Implement Persistent KV Store Serialization
Implement a persistent in-memory key-value store. Requirements: - Keys and values are arbitrary byte strings or UTF-8 strings; do not rely on delimite...
Implement a Cursor-Based Text Editor
Implement an in-memory text editor that maintains a mutable string and a cursor position between characters. The editor starts with an empty document ...
Min boards to cover roof holes
You are given an m x n binary grid roof representing a roof surface: - roof[i][j] = 1 means the cell is intact. - roof[i][j] = 0 means the cell is a h...
Simulate sticky load balancer with shutdown
Problem Implement a simulator for a load balancer that routes long-lived WebSocket connections across m backend servers. You receive a sequence of tex...
Maximize correct guesses in a hat line puzzle
Problem (Hat Guessing Strategy) There are N people standing in a line. Each person wears a hat that is either Red or Blue. - Person i can see the hats...
Compute org height and minimal CEO promotions
You are given an organization chart with n employees labeled 1..n. Employee 1 is the CEO (root). The reporting relationships are given as two integer ...
Find cheapest common ancestor in a tree
Coding You are given a rooted tree where each node has: - an integer price - a pointer to its parent (root has parent = null) - a list of children Giv...
Build span trees from unordered trace spans
You are given an unordered list of span objects. Each span is a map/dictionary containing at least: - span_id (string, unique) - parent_id (string or ...
Find smallest permutation under constraints
Given a non-negative integer n, consider its decimal digits as a multiset (digits can repeat). 1) Return the smallest possible integer that can be for...
Design LFU cache with distributed extension
Problem You are asked to design and implement a data structure that behaves like an in-memory cache with a Least Frequently Used (LFU) eviction policy...
Compute Latencies and Search Grid Path
You are given two coding tasks from an internship interview. Task 1: Compute Message Latency from CSV Logs Two systems, ComputeA and ComputeB, exchang...
Find shared courses between student pairs
Problem Set (Coding) You are given multiple coding questions from an interview. Implement each function as described. --- 1) Course Overlap You are gi...
Compute top-N items from log stream
Problem You are given application logs containing events with an itemId. Each log line may contain extra fields, but you can extract the itemId from e...
Rotate a 3×3 digit grid by 180°
Problem You are given a 3×3 grid of digits (characters '0'–'9'), represented as an array of 3 strings of length 3. When the entire grid is rotated by ...
Compute minutes since last train departure
You are given a daily train timetable as a list of departure times (24-hour format HH:MM). Given the current time (also HH:MM), find the most recent d...