Phase I — Linear Structures (Week 1)

1. Hash-Based Lookup — builds on nothing

Set	LC #	Problem
A	217	Contains Duplicate
A	242	Valid Anagram
A	1	Two Sum
A	49	Group Anagrams
A	347	Top K Frequent Elements
B	383	Ransom Note
B	205	Isomorphic Strings
B	128	Longest Consecutive Sequence
B	290	Word Pattern

2. Prefix Sum — builds on 1

Set	LC #	Problem
A	303	Range Sum Query
A	238	Product of Array Except Self
A	560	Subarray Sum Equals K
B	525	Contiguous Array
B	974	Subarray Sums Divisible by K

3. Two Pointers — builds on ordered iteration

Set	LC #	Problem
A	125	Valid Palindrome
A	167	Two Sum II
A	15	3Sum
A	11	Container With Most Water
A	42	Trapping Rain Water
B	392	Is Subsequence
B	977	Squares of a Sorted Array
B	189	Rotate Array
B	80	Remove Duplicates II

4. Sliding Window — builds on 3

Set	LC #	Problem
A	121	Best Time to Buy and Sell Stock
A	3	Longest Substring Without Repeating Characters
A	424	Longest Repeating Character Replacement
A	567	Permutation in String
A	76	Minimum Window Substring
B	209	Minimum Size Subarray Sum
B	1004	Max Consecutive Ones III
B	643	Maximum Average Subarray

5. Binary Search — builds on ordered/monotonic invariants

Set	LC #	Problem
A	704	Binary Search
A	74	Search a 2D Matrix
A	875	Koko Eating Bananas
A	33	Search in Rotated Sorted Array
A	153	Find Minimum in Rotated Sorted Array
B	35	Search Insert Position
B	162	Find Peak Element
B	34	First & Last Position
B ⭐	4	Median of Two Sorted Arrays

6. Stack — independent primitive

Set	LC #	Problem
A	20	Valid Parentheses
A	155	Min Stack
A	150	Evaluate Reverse Polish Notation
B	71	Simplify Path
B ⭐	224	Basic Calculator

7. Monotonic Stack — builds on 6

Set	LC #	Problem
A	739	Daily Temperatures
A	853	Car Fleet
B	496	Next Greater Element I
B	901	Online Stock Span
B ⭐	84	Largest Rectangle in Histogram

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Phase II — Nodal & Grid Structures (Week 2)

8. Linked List — independent primitive

Set	LC #	Problem
A	206	Reverse Linked List
A	21	Merge Two Sorted Lists
A	141	Linked List Cycle
A	19	Remove Nth Node From End
A	143	Reorder List
B	876	Middle of the Linked List
B	92	Reverse Linked List II
B	82	Remove Duplicates from Sorted List II
B	61	Rotate List
B	86	Partition List

9. Hybrid Structures — builds on 1 + 8

Set	LC #	Problem
A	146	LRU Cache
A	2	Add Two Numbers
B	138	Copy List with Random Pointer
B	380	Insert Delete GetRandom O(1)

10. Matrix Index Math — builds on 3

Set	LC #	Problem
A	48	Rotate Image
A	54	Spiral Matrix
A	73	Set Matrix Zeroes
B	36	Valid Sudoku
B	289	Game of Life

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Phase III — Hierarchical Structures (Week 3)

11. Tree DFS — builds on recursion

Set	LC #	Problem
A	226	Invert Binary Tree
A	104	Maximum Depth of Binary Tree
A	100	Same Tree
A	572	Subtree of Another Tree
A	236	Lowest Common Ancestor
A ⭐	124	Binary Tree Maximum Path Sum
B	101	Symmetric Tree
B	112	Path Sum
B	129	Sum Root to Leaf Numbers
B	543	Diameter of Binary Tree

12. Tree BFS — builds on 6's sibling (queue) + 11

Set	LC #	Problem
A	102	Level Order Traversal
A	199	Right Side View
A	1448	Count Good Nodes
B	103	Zigzag Level Order
B	637	Average of Levels

13. Binary Search Tree — builds on 5 + 11

Set	LC #	Problem
A	98	Validate BST
A	230	Kth Smallest in BST
A	235	LCA of BST
A	105	Build from Preorder + Inorder
B	530	Minimum Absolute Difference
B	173	BST Iterator
B	108	Sorted Array to BST

14. Heap / Priority Queue — builds on trees (implicit tree over array)

Set	LC #	Problem
A	215	Kth Largest in Array
A	703	Kth Largest in Stream
A	973	K Closest Points
A	621	Task Scheduler
A	23	Merge K Sorted Lists
B	1046	Last Stone Weight
B	373	K Pairs with Smallest Sums
B ⭐	295	Find Median from Data Stream
B ⭐	502	IPO

15. Trie — builds on 11

Set	LC #	Problem
A	208	Implement Trie
A	211	Add & Search Words
B	212	Word Search II (needs topic 20 — schedule after)

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Phase IV — Relational Structures (Week 4)

16. Graph DFS — builds on 11 + visited set

Set	LC #	Problem
A	200	Number of Islands
A	695	Max Area of Island
A	133	Clone Graph
A	417	Pacific Atlantic Water Flow
A	130	Surrounded Regions
B	399	Evaluate Division
B	261	Graph Valid Tree

17. Graph BFS — builds on 12 + visited set

Set	LC #	Problem
A	994	Rotting Oranges
A	127	Word Ladder
B	909	Snakes and Ladders
B	433	Minimum Genetic Mutation
B	286	Walls and Gates

18. Topological Sort — builds on 16

Set	LC #	Problem
A	207	Course Schedule
A	210	Course Schedule II
B ⭐	269	Alien Dictionary
B	1462	Course Schedule IV

19. Union-Find — builds on 16's problem class

Set	LC #	Problem
A	684	Redundant Connection
A	323	Number of Connected Components
B	128	Longest Consecutive (union-find variant)
B	721	Accounts Merge

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Phase V — Decision-Space Exploration (Weeks 4–5)

20. Backtracking — builds on 16

Set	LC #	Problem
A	78	Subsets
A	39	Combination Sum
A	46	Permutations
A	79	Word Search
B	17	Letter Combinations
B	77	Combinations
B	22	Generate Parentheses
B ⭐	52	N-Queens II

(Now unlock 212 Word Search II from topic 15.)

21. 1-D Dynamic Programming — builds on 20

Set	LC #	Problem
A	70	Climbing Stairs
A	746	Min Cost Climbing Stairs
A	198	House Robber
A	213	House Robber II
A	322	Coin Change
A	300	Longest Increasing Subsequence
B	139	Word Break
B	91	Decode Ways
B	647	Palindromic Substrings

22. Multi-D / Grid DP — builds on 21

Set	LC #	Problem
A	62	Unique Paths
A	64	Minimum Path Sum
A	1143	Longest Common Subsequence
B	120	Triangle
B	63	Unique Paths II
B ⭐	72	Edit Distance
B	221	Maximal Square
B ⭐	97	Interleaving String

23. Greedy — builds on 21

Set	LC #	Problem
A	53	Maximum Subarray (Kadane's)
A	55	Jump Game
A	45	Jump Game II
A	134	Gas Station
B	122	Best Time to Buy and Sell Stock II
B	918	Maximum Sum Circular Subarray
B	763	Partition Labels

24. Intervals — builds on 23

Set	LC #	Problem
A	57	Insert Interval
A	56	Merge Intervals
A	435	Non-Overlapping Intervals
A	253	Meeting Rooms II
B	228	Summary Ranges
B	452	Minimum Arrows to Burst Balloons
B	920	Meeting Rooms I