Coding Interview Prep

Coding Problems

300 problems organized by pattern and difficulty. Free tier includes 135 problems. Upgrade to Pro for all 300.

Two Pointers

Tree

Array

Dynamic Programming

Binary Search

SQL

Arrays

Hash Table

Math

String

Matrix

Intervals

Linked List

Stack

Bit Manipulation

Linked Lists

Sliding Window

Trees

Strings

Functions & Closures

Graphs

Hash Tables

Databases

Heaps

Functional Programming

Queues

Concurrency

Design Patterns

Graph

Backtracking

Greedy

Free Problems (135)

Title	Category	Difficulty
Backspace String Compare	Two Pointers	Easy
Balanced Binary Tree	Tree	Easy
Best Time to Buy and Sell Stock	Array	Easy
Best Time to Buy and Sell Stock	Dynamic Programming	Easy
Binary Search	Binary Search	Easy
Climbing Stairs	Dynamic Programming	Easy
Combine Two Tables	SQL	Easy
Concatenation of Array	Arrays	Easy
Contains Duplicate	Array	Easy
Contains Duplicate II	Hash Table	Easy
Counting Bits	Array	Easy
Diameter of Binary Tree	Tree	Easy
First Unique Character in a String	Hash Table	Easy
Happy Number	Hash Table	Easy
Happy Number Math	Math	Easy
Implement strStr()	String	Easy
Invert Binary Tree	Tree	Easy
Isomorphic Strings	Hash Table	Easy
Is Subsequence	String	Easy
Linked List Cycle	Two Pointers	Easy
Longest Common Prefix	String	Easy
Lucky Numbers in a Matrix	Matrix	Easy
Majority Element	Arrays	Easy
Maximum Depth of Binary Tree	Tree	Easy
Meeting Rooms	Intervals	Easy
Merge Sorted Array	Two Pointers	Easy
Merge Two Sorted Lists	Linked List	Easy
Missing Number	Array	Easy
Move Zeroes	Array	Easy
Next Greater Element I	Stack	Easy
Number of 1 Bits	Array	Easy
Palindrome Linked List	Linked List	Easy
Palindrome Number	Math	Easy
Path Sum	Tree	Easy
Plus One	Array	Easy
Ransom Note	Hash Table	Easy
Remove Duplicates from Sorted Array	Two Pointers	Easy
Remove Duplicates from Sorted List	Linked List	Easy
Remove Element	Two Pointers	Easy
Reverse Bits	Array	Easy
Reverse Linked List	Linked List	Easy
Roman to Integer	String	Easy
Same Tree	Tree	Easy
Search Insert Position	Binary Search	Easy
Single Number	Bit Manipulation	Easy
Sqrt(x)	Binary Search	Easy
Sqrt(x) Math	Math	Easy
Squares of a Sorted Array	Two Pointers	Easy
Subtree of Another Tree	Tree	Easy
Toeplitz Matrix	Matrix	Easy
Two Sum	Array	Easy
Valid Anagram	String	Easy
Valid Palindrome	String	Easy
Valid Palindrome II	Two Pointers	Easy
Valid Parentheses	String	Easy
Word Pattern	Hash Table	Easy
3Sum	Array	Medium
Agent Memory Manager	Linked Lists	Medium
Best Time to Buy and Sell Stock II	Sliding Window	Medium
Best Time to Buy and Sell Stock III	Dynamic Programming	Medium
Binary Search in Rotated Sorted Array	Arrays	Medium
Binary Search Tree Operations	Trees	Medium
Binary Search Tree Operations	Trees	Medium
Binary Tree Maximum Path Sum	Trees	Medium
COBOL Numeric Storage Decoder	Strings	Medium
Container With Most Water	Array	Medium
DB2 Cursor Statement Validator	Strings	Medium
Debounce Function	Functions & Closures	Medium
Dining Philosophers: Deadlock-Free Resource Allocation	Graphs	Medium
Distributed Rate Limiter	Hash Tables	Medium
Distributed Rate Limiter	Hash Tables	Medium
Duplicate Insert Error Handler	Hash Tables	Medium
Employees Earning More Than Their Manager	Databases	Medium
Employees Earning More Than Their Manager	Databases	Medium
Find Median from Data Stream	Heaps	Medium
Find Minimum in Rotated Sorted Array	Array	Medium
Find the Duplicate Number	Array	Medium
Group Anagrams	String	Medium
High-Frequency Claimants	Databases	Medium
Implement Debounce	Functional Programming	Medium
Island Perimeter	Graphs	Medium
JCL Job Step Sequencer for COBOL File Processing	Strings	Medium
Job Log Analyzer	Hash Tables	Medium
K Closest Hotels	Heaps	Medium
K Closest Hotels	Trees	Medium
Kth Smallest Element in a BST	Trees	Medium
Longest Common Subsequence	Dynamic Programming	Medium
Longest Substring Without Repeating Characters	String	Medium
Loop Simulation: UNTIL vs VARYING	Strings	Medium
LRU Cache	Linked Lists	Medium
LRU Cache	Linked Lists	Medium
Maximum Product Subarray	Array	Medium
Maximum Subarray	Array	Medium
Maximum Sum Subarray of Size K	Arrays	Medium
Median of Two Sorted Arrays	Arrays	Medium
Memoization Cache Simulator	Hash Tables	Medium
Memoization Cache Simulator	Hash Tables	Medium
Merge Two Sorted Linked Lists	Linked Lists	Medium
Module Call Resolver	Arrays	Medium
Net Revenue Per Account	Hash Tables	Medium
Network Shortest Path	Graphs	Medium
Next Permutation	Arrays	Medium
Pair Sum Finder	Hash Tables	Medium
Payment API Rate Limiter	Hash Tables	Medium
Peak Concurrent Bookings	Arrays	Medium
Peak Concurrent Bookings	Arrays	Medium
Product Inventory REST API	Strings	Medium
Product of Array Except Self	Array	Medium
Prompt Strategy Classifier	Arrays	Medium
Rate Limiter for Hotel Search API	Hash Tables	Medium
ReAct Agent Simulator	Strings	Medium
Real-Time Transaction Anomaly Detector	Hash Tables	Medium
Request Scheduler: Minimum Threads for Concurrent Processing	Graphs	Medium
Reverse Words in a String	String	Medium
Rotate Array	Array	Medium
Rotate Matrix 90 Degrees Clockwise	Arrays	Medium
Search in Rotated Sorted Array	Array	Medium
Serialize and Deserialize Binary Tree	Trees	Medium
Shared Memory Parameter Passing	Arrays	Medium
Shortest Path in Binary Matrix	Graphs	Medium
Sort Colors	Two Pointers	Medium
Stock Trader with K Transactions	Dynamic Programming	Medium
Subarray Sum Equals K with Bounded Window	Arrays	Medium
Suspicious Transaction Detector	Hash Tables	Medium
Suspicious Transaction Detector	Strings	Medium
Task Scheduler Simulator	Queues	Medium
Task Scheduler with Dependencies	Graphs	Medium
Thread-Safe Bounded Producer-Consumer Queue	Concurrency	Medium
Thread-Safe Singleton	Design Patterns	Medium
Thread-Safe Singleton Logger	Concurrency	Medium
Top 3 Most Booked Hotel Categories	Hash Tables	Medium
Top K Frequent Transactions	Hash Tables	Medium
Transaction Deduplication	Hash Tables	Medium
Two Sum II - Input Array Is Sorted	Hash Table	Medium
Visa Application Processing Order	Graphs	Medium

Premium Problems (165)

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