Case File Library

Work through LeetCode-style data structure and algorithm investigations that teach you how to read problem statements, follow constraints, eliminate suspects, qualify candidates, and prove the correct solution before writing code.

Public Preview Case Files #001-#003

#001 Target Element

Open Case File

#002 Two Sum

#003 Two Sum II

Starter Plan Case Files #004-#025

#004 3 Sum

#005 Sliding Window

#006 Minimum Window

#007 House Robber

#008 Clone Graph

#009 Coin Change

#010 Level Order Traversal

#011 Valid Parentheses

#012 Daily Temperatures

#013 Merge Intervals

#014 Search in Rotated Sorted Array

#015 Kth Largest Element

#016 Top K Frequent Elements

#017 Number of Islands

#018 Course Schedule

#019 Lowest Common Ancestor

#020 Validate Binary Search Tree

#021 Subsets

#022 Combination Sum

#023 Longest Increasing Subsequence

#024 Edit Distance

#025 Word Break

Student Plan Case Files #026-#050

#026 Reverse Linked List

#027 Linked List Cycle

#028 Merge K Sorted Lists

#029 LRU Cache

#030 Trapping Rain Water

#031 Largest Rectangle in Histogram

#032 Find Median from Data Stream

#033 Implement Trie

#034 Word Search II

#035 Accounts Merge

#036 Network Delay Time

#037 Cheapest Flights Within K Stops

#038 Min Cost to Connect All Points

#039 Serialize and Deserialize Binary Tree

#040 Binary Tree Maximum Path Sum

#041 Kth Smallest Element in a BST

#042 Construct Tree from Traversals

#043 N-Queens

#044 Palindrome Partitioning

#045 Decode Ways

#046 Partition Equal Subset Sum

#047 Longest Common Subsequence

#048 Burst Balloons

#049 Regular Expression Matching

#050 Alien Dictionary

#051 Contains Duplicate

#052 Product of Array Except Self

#053 Maximum Subarray

#054 Maximum Product Subarray

#055 Find Minimum in Rotated Sorted Array

#056 Container With Most Water

#057 Sum of Two Integers

#058 Number of 1 Bits

#059 Counting Bits

#060 Missing Number

#061 Reverse Bits

#062 Climbing Stairs

#063 Unique Paths

#064 Jump Game

#065 Longest Repeating Character Replacement

#066 Group Anagrams

#067 Longest Consecutive Sequence

#068 Insert Interval

#069 Non-overlapping Intervals

#070 Meeting Rooms II

#071 Remove Nth Node From End of List

#072 Same Tree

#073 Subtree of Another Tree

#074 Invert Binary Tree

#075 Pacific Atlantic Water Flow

Pro Plan Case Files #076-#150

#076 Minimum Size Subarray Sum

#077 Longest Substring Without Repeating Characters

#078 Permutation in String

#079 Find All Anagrams in a String

#080 Longest Substring with At Most K Distinct Characters

#081 4 Sum

#082 3 Sum Closest

#083 Container With Most Water II

#084 Valid Palindrome II

#085 Trapping Rain Water II

#086 Find K Closest Elements

#087 Kth Largest Element in an Array

#088 Top K Frequent Words

#089 Merge K Sorted Arrays

#090 Sliding Window Maximum

#091 Word Ladder

#092 Word Ladder II

#093 Reconstruct Itinerary

#094 Critical Connections in a Network

#095 Redundant Connection II

#096 Number of Connected Components

#097 Graph Valid Tree

#098 Satisfiability of Equality Equations

#099 Number of Provinces

#100 Similar String Groups

#101 Best Time to Buy and Sell Stock III

#102 Best Time to Buy and Sell Stock IV

#103 House Robber II

#104 Decode Ways II

#105 Wildcard Matching

#106 Regular Expression Matching II

#107 Interleaving String

#108 Distinct Subsequences

#109 Dungeon Game

#110 Minimum Path Sum II

#111 Binary Tree Serialization Compression

#112 Vertical Order Traversal

#113 Binary Tree Cameras

#114 Maximum Width of Binary Tree

#115 Recover Binary Search Tree

#116 Median of Two Sorted Arrays

#117 Search a 2D Matrix II

#118 Find Peak Element

#119 Capacity To Ship Packages Within D Days

#120 Split Array Largest Sum

#121 Sudoku Solver

#122 Restore IP Addresses

#123 Expression Add Operators

#124 Letter Tile Possibilities

#125 Matchsticks to Square

#126 Implement strStr (KMP)

#127 Longest Palindromic Substring

#128 Longest Palindromic Subsequence

#129 Shortest Palindrome

#130 Text Justification

#131 Spiral Matrix II

#132 Rotate Image

#133 Set Matrix Zeroes

#134 Game of Life

#135 Maximal Rectangle

#136 LFU Cache

#137 All O(1) Data Structure

#138 Randomized Set

#139 Insert Delete GetRandom O(1)

#140 Design Twitter

#141 Design LRU Cache II

#142 Design Browser History

#143 Design Underground System

#144 Time Based Key Value Store

#145 Snapshot Array

#146 Median Finder Architecture

#147 Data Stream as Disjoint Intervals

#148 Sliding Window Median

#149 Minimum Cost Maximum Flow

#150 The Skyline Problem

Case File Library

Case Files

Each Case File adds a new reasoning move to your CCF toolkit.

Foundation Layer

Structural Pattern Layer

Window and Range Layer

Stack, Interval, and Control Layer

Graph, Recursion, and Advanced State Layer

Chapter 01 Learn the Basics Public Preview

Chapter 02 Anchor Frames and Window Movement Starter Plan

Chapter 03 State Memory and Decision Carryover Starter Plan

Chapter 04 Trees, Stacks, and Structural Validation Starter Plan

Chapter 05 Intervals, Search, and Selection Starter Plan

Chapter 06 Frequency, Graph Regions, and Dependencies Starter Plan

Chapter 07 Binary Tree Proofs Starter Plan

Chapter 08 Backtracking and Word Decisions Starter Plan

Chapter 09 String Decisions Starter Plan

Chapter 10 Linked Lists and Pointer Identity Student Plan

Chapter 11 Advanced Lists and Cache State Student Plan

Chapter 12 Monotonic Structures and Streams Student Plan

Chapter 13 Trie Search and Graph Union Student Plan

Chapter 14 Weighted Graph Decisions Student Plan

Chapter 15 Advanced Tree Reasoning Student Plan

Chapter 16 Backtracking Mastery Student Plan

Chapter 17 Dynamic Programming Fluency Student Plan

Chapter 18 Hard Pattern Integration Student Plan

Chapter 19 Array Fundamentals Student Plan

Chapter 20 Products, Rotation, and Boundaries Student Plan

Chapter 21 Bit Logic and Missing Evidence Student Plan

Chapter 22 Bit Completion and Stair Decisions Student Plan

Chapter 23 Grid Paths and Greedy Reach Student Plan

Chapter 24 Hashing and Sequence Groups Student Plan

Chapter 25 Scheduling and Linked Lists Student Plan

Chapter 26 Tree Recognition Student Plan

Chapter 27 Final Investigation Student Plan

Chapter 28 Advanced Sliding Window & Sequence Control Pro Plan

Chapter 29 Advanced Two Pointer Reasoning Pro Plan

Chapter 30 Advanced Heap & Priority Queue Decisions Pro Plan

Chapter 31 Advanced Graph Traversal Pro Plan

Chapter 32 Union Find Mastery Pro Plan

Chapter 33 Advanced Dynamic Programming Pro Plan

Chapter 34 DP Optimization & Mathematical States Pro Plan

Chapter 35 Advanced Tree Algorithms Pro Plan

Chapter 36 Advanced Binary Search Pro Plan

Chapter 37 Advanced Backtracking Pro Plan

Chapter 38 String Algorithms Pro Plan

Chapter 39 Advanced Matrix & Grid Algorithms Pro Plan

Chapter 40 Algorithm Optimization Challenges Pro Plan

Chapter 41 Advanced Systems Algorithms Pro Plan

Chapter 42 Expert Reasoning Challenges Pro Plan