Mock interviews

Real sandboxed coding rounds

Practice history →

Timed, hands-on problems checked against a hidden test suite — the formats companies actually run in interviews, not a generic algorithm quiz. Build something from scratch, or find and fix a real bug in code that's already there.

Thread-Safe Counter

Build the PrimitiveMedium

Contains Duplicate

Build the PrimitiveEasy

Fix: Deduplicate While Preserving Order

Debug the CodebaseEasy

Valid Anagram

Build the PrimitiveEasy

Two Sum

Build the PrimitiveEasy

Group Anagrams

Build the PrimitiveMedium

Top K Frequent Elements

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Product of Array Except Self

Build the PrimitiveMedium

Encode and Decode Strings

Build the PrimitiveMedium

Valid Sudoku

Build the PrimitiveMedium

Longest Consecutive Sequence

Build the PrimitiveMedium

Merge Booking Windows

Build the PrimitiveEasy

Valid Palindrome

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Rolling Maximum

Build the PrimitiveMedium

Two Sum II — Sorted Input

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Kth Largest in a Stream

Build the PrimitiveMedium

3Sum

Build the PrimitiveMedium

Suppress Duplicate Alerts

Build the PrimitiveMedium

Container With Most Water

Build the PrimitiveMedium

Fix: The Invoice That Does Not Balance

Debug the CodebaseMedium

Trapping Rain Water

Build the PrimitiveHard

Fix: The Page That Skips Rows

Debug the CodebaseEasy

Best Time to Buy and Sell Stock

Build the PrimitiveEasy

Longest Substring Without Repeating Characters

Build the PrimitiveMedium

Longest Repeating Character Replacement

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Permutation in String

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Minimum Window Substring

Build the PrimitiveHard

Sliding Window Maximum

Build the PrimitiveHard

Valid Parentheses

Build the PrimitiveEasy

Min Stack

Build the PrimitiveMedium

Evaluate Reverse Polish Notation

Build the PrimitiveMedium

Daily Temperatures

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Largest Rectangle in Histogram

Build the PrimitiveHard

Binary Search

Build the PrimitiveEasy

Search a 2D Matrix

Build the PrimitiveMedium

Koko Eating Bananas

Build the PrimitiveMedium

Find Minimum in Rotated Sorted Array

Build the PrimitiveMedium

Search in Rotated Sorted Array

Build the PrimitiveMedium

Median of Two Sorted Arrays

Build the PrimitiveHard

Reverse Linked List

Build the PrimitiveEasy

Merge Two Sorted Lists

Build the PrimitiveEasy

Linked List Cycle

Build the PrimitiveEasy

Remove Nth Node From End of List

Build the PrimitiveMedium

Reorder List

Build the PrimitiveMedium

Copy List with Random Pointer

Build the PrimitiveMedium

LRU Cache

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Merge k Sorted Lists

Build the PrimitiveHard

Invert Binary Tree

Build the PrimitiveEasy

Maximum Depth of Binary Tree

Build the PrimitiveEasy

Diameter of Binary Tree

Build the PrimitiveEasy

Subtree of Another Tree

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Lowest Common Ancestor of a BST

Build the PrimitiveMedium

Binary Tree Level Order Traversal

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Binary Tree Right Side View

Build the PrimitiveMedium

Validate Binary Search Tree

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Kth Smallest Element in a BST

Build the PrimitiveMedium

Binary Tree Maximum Path Sum

Build the PrimitiveHard

Serialize and Deserialize Binary Tree

Build the PrimitiveHard

Implement Trie

Build the PrimitiveMedium

Design Add and Search Words

Build the PrimitiveMedium

Word Search II

Build the PrimitiveHard

Kth Largest Element in a Stream

Build the PrimitiveEasy

Last Stone Weight

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K Closest Points to Origin

Build the PrimitiveMedium

Kth Largest Element in an Array

Build the PrimitiveMedium

Find Median from Data Stream

Build the PrimitiveHard

Subsets

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Combination Sum

Build the PrimitiveMedium

Permutations

Build the PrimitiveMedium

Word Search

Build the PrimitiveMedium

Palindrome Partitioning

Build the PrimitiveMedium

N-Queens

Build the PrimitiveHard

Number of Islands

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Max Area of Island

Build the PrimitiveMedium

Clone Graph

Build the PrimitiveMedium

Rotting Oranges

Build the PrimitiveMedium

Surrounded Regions

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Pacific Atlantic Water Flow

Build the PrimitiveMedium

Course Schedule

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Course Schedule II

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Graph Valid Tree

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Network Delay Time

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Cheapest Flights Within K Stops

Build the PrimitiveMedium

Alien Dictionary

Build the PrimitiveHard

Climbing Stairs

Build the PrimitiveEasy

House Robber

Build the PrimitiveMedium

House Robber II

Build the PrimitiveMedium

Longest Palindromic Substring

Build the PrimitiveMedium

Coin Change

Build the PrimitiveMedium

Longest Increasing Subsequence

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Word Break

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Maximum Product Subarray

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Unique Paths

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Longest Common Subsequence

Build the PrimitiveMedium

Best Time to Buy and Sell Stock with Cooldown

Build the PrimitiveMedium

Target Sum

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Edit Distance

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Maximum Subarray

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Jump Game

Build the PrimitiveMedium

Jump Game II

Build the PrimitiveMedium

Gas Station

Build the PrimitiveMedium

Insert Interval

Build the PrimitiveMedium

Merge Intervals

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Non-overlapping Intervals

Build the PrimitiveMedium

Meeting Rooms II

Build the PrimitiveMedium

Single Number

Build the PrimitiveEasy

Number of 1 Bits

Build the PrimitiveEasy

Sum of Two Integers

Build the PrimitiveMedium