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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Find LCA in a BST
Given the root of a binary search tree and two keys p and q, return the value of their lowest common ancestor (the deepest node whose value lies betwe...
Determine earliest collision among moving cars
You are given n cars moving over time. Each car has known initial state at time \(t=0\): - 1D case (straight road): - initial position \(x_i\) (mete...
Design an IR for test workflows
Design an intermediate representation (IR) for a graphics testing workflow as a DAG. Define node/edge types, metadata, and side-effect modeling. Expla...
Validate 9x9 grid in one pass
Given a partially filled 9x9 board using digits '1'–'9' and '.' for empty cells, determine whether the current configuration is valid under Sudoku rul...
Implement an LRU cache
Implement a fixed-capacity key-value cache with least-recently-used eviction. Support the following operations: - get(key) -> value: return the value ...
Implement FizzBuzz
Write a function that takes an integer n and outputs the numbers from 1 to n using the standard FizzBuzz rules: - output Fizz for numbers divisible by...
Implement a Task Processor
Design a task processor that supports two operations: - AddTask(task): add a new task. - ConsumeTask(): remove and return the id of the next task to e...
Design an in-memory cloud storage system
Design and implement an in-memory cloud storage system that maps file paths to metadata and supports multi-user quotas. Use simple data structures; pe...
Compute minimal flips connecting two islands
Given an n x n binary grid of 0s (water) and 1s (land) containing exactly two disjoint islands (cells with 1 connected 4-directionally), return the mi...
Count inversions in an array efficiently
Given the array [5, 7, 9, 2, 3, 12, 8, 4], compute the number of inversion pairs (i, j) where i < j and arr[i] > arr[j]. Describe both a naive O(n^ 2)...
Find connected region sizes in matrix
Given an m x n grid of characters grid and a target character ch, implement: ( 1) sizeOfRegion(grid, r0, c0, ch) -> int that returns the size of the 4...
Implement tree traversals, BFS, and subsets generation
1) Define a TreeNode class for a binary tree with an integer value and left/right pointers. Implement preorder, inorder, and postorder traversals: (a)...
Simulate views on an n-ary tree
Given a rooted, ordered n-ary tree (each node has a value and an ordered list of children), simulate an observer who starts at the bottom-left, moves ...
Compute shared free time intervals
You are given schedules for multiple employees. schedules[i] is a list of busy intervals for employee i, where each interval is half-open [start, end)...
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...
Simulate one-round color elimination on a grid
Given an m x n integer matrix board where board[r][c] > 0 represents a color and 0 represents empty: ( 1) A nonzero cell at (r,c) explodes in this rou...
Check path in N-ary tree
Given the root of an N-ary tree and a sequence of integers path[0..k-1], determine whether there exists a path starting at the root whose node values ...
Implement DFS and tree algorithms
Part 1 (DFS on graph): Given an undirected graph with n nodes labeled 0..n-1 and an edge list, implement a function that returns all connected compone...
Find >n/3 elements in sorted array
Question Given a sorted (non-decreasing) integer array A of length n, return all distinct values that occur strictly more than n/3 times. Design an al...
Find substring where all chars appear at least k
You are given a string s and an integer k (1 ≤ k ≤ |s|). Return the length of the longest substring in which every distinct character occurs at least ...