Coding Trainer

Practice algorithmic exercises with spaced repetition.

Start a Practice Session

Difficulty

Number of exercises (133 available)

Roadmap

0 / 1330%

Foundations0/4

Prefix Sum0/3

Two Pointers0/3

Sliding Window0/14

Fast & Slow Ptrs0/3

Linked Lists0/7

Monotonic Stack0/3

Top K / Heap0/3

Sorting & Greedy0/8

Intervals0/3

Binary Search0/7

Backtracking0/3

Binary Tree0/4

DFS0/3

BFS0/3

Matrix0/5

Strings & DP0/3

Dynamic Prog.0/5

Design0/1

ML & Systems0/4

Easy Medium Hard· Click any exercise to toggle completion

Exercise Bank (133)

Two Sum

Hash Map Lookup

Maximum Average Subarray

Longest Substring Without Repeating Characters

Sliding WindowHash Map Lookup

Valid Parentheses

Merge Intervals

Search in Rotated Sorted Array

Number of Islands

Trees & Graph Traversal (BFS/DFS)

LRU Cache

Hash Map Lookup

Implement Softmax from Scratch

Transformer Architecture

Scaled Dot-Product Attention

Transformer Architecture

Design a Rate Limiter

System Design Fundamentals

Design an LLM Inference Service

System Design FundamentalsTransformer ArchitectureTokenization & BPE

Median of Two Sorted Arrays

Longest Palindromic Substring

Integer to Roman

Greedy Algorithms

Remove Nth Node From End of List

Linked List PatternsTwo Pointers

Merge k Sorted Lists

Heap / Priority QueueLinked List Patterns

Reverse Nodes in k-Group

Linked List Patterns

Permutations

Pow(x, n)

Fast Exponentiation

Minimum Window Substring

Sliding WindowHash Map Lookup

Remove Duplicates from Sorted Array II

Remove Duplicates from Sorted List II

Linked List Patterns

Climbing Stairs

Dynamic Programming

Split Array Largest Sum

Task Scheduler

Greedy Algorithms

Wildcard Matching

String Dynamic ProgrammingDynamic Programming

Bag of Tokens

Two PointersGreedy Algorithms

Spiral Matrix

Matrix Traversal & In-Place Operations

Kth Smallest Element in Sorted Matrix

Rotate Image

Matrix Traversal & In-Place Operations

Minimum Path Sum

Dynamic Programming

Remove Duplicates from Sorted Array

Repeated DNA Sequences

Sliding WindowHash Map Lookup

Minimum Size Subarray Sum

Longest Substring with At Least K Repeating Characters

Arithmetic Slices

Sliding WindowDynamic Programming

Longest Repeating Character Replacement

Sliding WindowHash Map Lookup

Find All Anagrams in a String

Sliding WindowHash Map Lookup

Permutation in String

Sliding WindowHash Map Lookup

Find K Closest Elements

Binary SearchSliding Window

Fruit Into Baskets

Sliding WindowHash Map Lookup

Count Number of Nice Subarrays

Sliding WindowPrefix Sum

Jump Game

Greedy Algorithms

Jump Game II

Greedy Algorithms

Gas Station

Greedy Algorithms

Hand of Straights

Greedy Algorithms

Non-overlapping Intervals

Greedy Algorithms

Range Sum Query - Immutable

LC #303

Contiguous Array

Prefix SumHash Map Lookup

LC #525

Subarray Sum Equals K

Prefix SumHash Map Lookup

LC #560

Two Sum II - Input Array Is Sorted

LC #167

3Sum

LC #15

Container With Most Water

LC #11

Linked List Cycle

Fast & Slow Pointers

LC #141

Happy Number

Fast & Slow Pointers

LC #202

Find the Duplicate Number

Fast & Slow Pointers

LC #287

Reverse Linked List

Linked List Reversal

LC #206

Reverse Linked List II

Linked List Reversal

LC #92

Swap Nodes in Pairs

Linked List Reversal

LC #24

Next Greater Element I

Monotonic Stack

LC #496

Daily Temperatures

Monotonic Stack

LC #739

Largest Rectangle in Histogram

Monotonic Stack

LC #84

Kth Largest Element in an Array

LC #215

Top K Frequent Elements

LC #347

Find K Pairs with Smallest Sums

LC #373

Insert Interval

LC #57

Find Minimum in Rotated Sorted Array

LC #153

Search a 2D Matrix II

LC #240

Binary Tree Paths

LC #257

Kth Smallest Element in a BST

LC #230

Binary Tree Maximum Path Sum

LC #124

Binary Tree Level Order Traversal II

LC #107

Clone Graph

LC #133

Path Sum II

LC #113

Course Schedule II

Topological Sort

LC #210

Binary Tree Level Order Traversal

LC #102

Rotting Oranges

LC #994

Word Ladder

LC #127

Flood Fill

Matrix Traversal

LC #733

Surrounded Regions

Matrix Traversal

LC #130

Subsets

LC #78

N-Queens

LC #51

Longest Increasing Subsequence

Dynamic Programming

LC #300

Coin Change

0/1 Knapsack (DP)Dynamic Programming

LC #322

Partition Equal Subset Sum

0/1 Knapsack (DP)Dynamic Programming

LC #416

Longest Common Subsequence

Dynamic Programming

LC #1143

Burst Balloons

Dynamic Programming

LC #312

Best Time to Buy and Sell Stock

Greedy Algorithms

LC #121

Contains Duplicate

Hash Map Lookup

LC #217

Product of Array Except Self

LC #238

Maximum Subarray

Dynamic Programming

LC #53

Maximum Product Subarray

Dynamic Programming

LC #152

Sum of Two Integers

LC #371

Number of 1 Bits

LC #191

Counting Bits

Dynamic Programming

LC #338

Missing Number

LC #268

Reverse Bits

LC #190

Word Break

Dynamic ProgrammingString Dynamic Programming

LC #139

Combination Sum

LC #39

House Robber

Dynamic Programming

LC #198

House Robber II

Dynamic Programming

LC #213

Course Schedule

Topological Sort

LC #207

Pacific Atlantic Water Flow

Matrix Traversal & In-Place Operations

LC #417

Longest Consecutive Sequence

Hash Map Lookup

LC #128

Alien Dictionary

Topological Sort

LC #269

Graph Valid Tree

LC #261

Number of Connected Components in an Undirected Graph

LC #323

Meeting Rooms

LC #252

Meeting Rooms II

LC #253

Merge Two Sorted Lists

Linked List Patterns

LC #21

Reorder List

Linked List Patterns

LC #143

Set Matrix Zeroes

Matrix Traversal & In-Place Operations

LC #73

Word Search

LC #79

Decode Ways

Dynamic ProgrammingString Dynamic Programming

LC #91

Unique Paths

Dynamic Programming

LC #62

Valid Anagram

Hash Map Lookup

LC #242

Group Anagrams

Hash Map Lookup

LC #49

Valid Palindrome

LC #125

Palindromic Substrings

LC #647

Encode and Decode Strings

LC #271

Maximum Depth of Binary Tree

Trees & Graph Traversal (BFS/DFS)

LC #104

Same Tree

Trees & Graph Traversal (BFS/DFS)

LC #100

Invert Binary Tree

Trees & Graph Traversal (BFS/DFS)

LC #226

Serialize and Deserialize Binary Tree

Trees & Graph Traversal (BFS/DFS)

LC #297

Subtree of Another Tree

Trees & Graph Traversal (BFS/DFS)

LC #572

Construct Binary Tree from Preorder and Inorder Traversal

Trees & Graph Traversal (BFS/DFS)

LC #105

Validate Binary Search Tree

Trees & Graph Traversal (BFS/DFS)

LC #98

Lowest Common Ancestor of a Binary Search Tree

Trees & Graph Traversal (BFS/DFS)

LC #235

Implement Trie (Prefix Tree)

LC #208

Add and Search Word

LC #211

Word Search II

LC #212

Find Median from Data Stream

Heap / Priority Queue

LC #295

Knowledge Bank (20)