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."
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Implement expression expansion to plus-only form
Given a string expression consisting only of lowercase letters (variables), '+', '*', '(', and ')', return an equivalent expression that uses only '+'...
Compute waits and find distance-k node pairs
Part 1 — Array next-higher wait: Given an integer array A where A[i] is the measurement for day i (0-indexed), return an array W of the same length su...
Maintain k-th largest in a stream
Design and implement a class KthLargest that, given an integer k and an initial list of integers, supports: ( 1) KthLargest(k, nums): constructor; ( 2...
Implement sorting and set intersection with input parsing
Write two functions and explain your approach in under two minutes after coding: (A) Sorting: Implement sort_numbers(nums: List[int]) -> List[int] tha...
Plot ASCII chart for time-price pairs
Given an unsorted array of (timestamp, price) integer pairs, write a function to render an ASCII chart of the time series. The x-axis must include eve...
Compute left and right views once
Given the root of a binary search tree, output two lists: the nodes visible from the left side and the nodes visible from the right side, from top to ...
Navigate unknown maze to find target
You are given an exploration interface for an unknown 2D maze that exposes only local actions (e.g., move(up/down/left/right) -> bool indicating succe...
Find two numbers summing to target
Given an unsorted integer array and a target value, return the indices of two distinct elements whose sum equals the target. Aim for an O(n) time solu...
Implement Union-Find and track components
Implement a Disjoint Set Union (Union-Find) data structure with union by rank and path compression. Design the API to support union(a, b), connected(a...
Implement exponentiation and link tree neighbors
Solve two independent tasks. Task A — Fast exponentiation: Implement fastExponent(x, n) that returns x raised to the integer power n, where x is a dou...
Design mutable sum-tree with fast queries
You're given a rooted, mutable tree. Each leaf node stores an integer value. Each internal node's value equals the sum of its immediate children's val...
Solve word segmentation and React palindrome validation
Part A — String segmentation: Given a non-empty string s and a dictionary of valid words, design an algorithm to determine whether s can be segmented ...
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...
Find top-K frequent values with tiebreaks
Question Given an integer array nums and an integer k, return the k values with the highest frequency. The array can contain up to 10^6 elements. When...
Solve tree partition and IPO allocation
1) Tree partitioning for minimum difference: Given a rooted tree as an array parent of length n (parent[i] gives the parent of node i, and parent[root...
Merge overlapping and adjacent ranges
Given an unsorted list of integer ranges represented as half-open intervals [start, end) with start < end, merge all overlapping or directly adjacent ...
Compute delivery wait times
You're building a last‑mile delivery simulator. Given n orders, each with arrival_time (non-decreasing integers) and service_time (positive integers),...
Compute rooms and verify tree completeness
This question has two independent algorithm problems on a single calendar/tree theme. Treat each Part as a self-contained coding exercise: implement a...
Check near-palindrome with one deletion
Given a string s, determine if it can become a palindrome after deleting at most one character. Return true or false and provide time and space comple...
Reverse between equal-value nodes in list
Given the head of a singly linked list and a target value v, locate the first two nodes whose values equal v (call them A and B, with A before B) and ...