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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"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."
Solve Open the Lock BFS
Question LeetCode 752. Open the Lock – Given an initial lock state "0000", a target combination, and a list of deadend combinations that cannot be use...
Compute max-ons and deletion indices
Question Given a circular array of n computers represented by 0 (off) and 1 (on), determine the maximum possible number of on computers within any con...
Maximize vacation streak with PTO
Question Given an array of characters containing 'w' (workday) and 'h' (holiday) and an integer n representing the number of PTO days you can convert ...
Critique and Test Python Preprocessing Utilities Effectively
Scenario Code review of Python preprocessing utilities (OutlierHandler and three Imputer classes) Question Summarize, at a high level, what the Outlie...
Sort and Rearrange: Efficient Algorithms for Diverse Challenges
Scenario Coding rounds and infrastructure-style algorithm questions. Question Write an efficient algorithm to return the length of the longest increas...
Implement BFS to Find Shortest Path in Graph
Scenario Social network needs to compute the shortest friend-distance between two users in an undirected graph containing millions of nodes. Question ...
Implement Reservoir Sampling; Analyze Time and Space Complexity
Scenario Process an unbounded stream of user IDs and maintain a uniform random sample of k users in memory. Question Implement reservoir sampling for ...
Parse Markdown Links Without Regex
Implement a function that converts simplified link syntax text into an HTML anchor tag <a href="url">text</a> across an entire input string. Constrain...
Solve stock-pattern trading and substring elimination
Part A — Stock trading by pattern signals: - Input: an integer array prices (length n) of daily stock prices; an array buyPattern and an array sellPat...
Compute longest palindromic subsequence
Given a string s (1 ≤ |s| ≤ 2000), implement a function that returns the length of the longest subsequence of s that reads the same forward and backwa...
Decide reachability with buses and limited walking
You are given: ( 1) a start point (xs, ys), ( 2) an end point (xe, ye), ( 3) an integer K, and ( 4) an undirected graph of bus stations where each nod...
Design rolling-window top-K click tracker
You receive a high-volume stream of click events (timestamp in ms, url). Implement a data structure with two operations: 1) record(event) inserts one ...
Design an IP filter using CIDR rules
Explain CIDR notation with a couple of concrete examples. Show how to convert a prefix like 192.168.0.0/16 into an inclusive 32-bit integer range and ...
Implement file word count
Write a function that reads a large text file and returns the frequency count of each word. Define how you will normalize tokens (case, Unicode, punct...
Analyze time and space complexity
For any algorithm you implement, analyze its time and space complexity using Big-O notation. Derive and justify the best, average, and worst-case comp...
Describe Java 8 features
What are the key new features introduced in Java 8? Explain when and how you would use lambda expressions, the Stream API, Optional, default methods o...
Implement basic calculator
Question LeetCode 227. Basic Calculator II – implement an arithmetic expression evaluator supporting +, -, *, / and integer operands https://leetcode....
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...
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 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 ...