PROBLEMS/TREES

Trees LeetCode Problems

253 hand-tagged Trees problems across 5 interview patterns (DFS Traversal (Inorder, Preorder, Postorder), BFS / Level-Order Traversal, BST Operations (Insert, Delete, Validate), Lowest Common Ancestor, Path Sum Problems), ranked by importance (how often each pattern shows up in real coding interviews). Work top-down within each pattern.

DFS Traversal (Inorder, Preorder, Postorder)

184 problems →

#	PROBLEM	DIFF	ELO	IMP	PATTERNS
1	Serialize and Deserialize Binary Tree	Medium	1672	89	BFS / Level-Order Traversal · Frequency Counting / Hash Map Lookup
2	Maximum Depth of Binary Tree	Easy	1028	88	BFS / Level-Order Traversal
3	Binary Tree Inorder Traversal	Easy	1048	88
4	Invert Binary Tree	Easy	1112	88	BFS / Level-Order Traversal
5	Diameter of Binary Tree	Easy	1267	88

+ 179 more DFS Traversal (Inorder, Preorder, Postorder) problems →

BFS / Level-Order Traversal

34 problems →

#	PROBLEM	DIFF	ELO	IMP	PATTERNS
1	Binary Tree Level Order Traversal	Easy	1195	92
2	Binary Tree Right Side View	Easy	1337	85	DFS Traversal (Inorder, Preorder, Postorder)
3	Amount of Time for Binary Tree to Be Infected	Medium	1711	74	BFS Shortest Path (Unweighted) · DFS Traversal (Inorder, Preorder, Postorder)
4	N-ary Tree Level Order Traversal	Easy	1198	73
5	All Nodes Distance K in Binary Tree	Medium	1663	72	DFS Traversal (Inorder, Preorder, Postorder) · Frequency Counting / Hash Map Lookup

+ 29 more BFS / Level-Order Traversal problems →

BST Operations (Insert, Delete, Validate)

19 problems →

#	PROBLEM	DIFF	ELO	IMP	PATTERNS
1	Validate Binary Search Tree	Easy	1342	90	DFS Traversal (Inorder, Preorder, Postorder)
2	Delete Node in a BST	Medium	1476	82	DFS Traversal (Inorder, Preorder, Postorder)
3	Insert into a Binary Search Tree	Easy	1152	78
4	Construct Binary Search Tree from Preorder Traversal	Medium	1563	72	DFS Traversal (Inorder, Preorder, Postorder) · Monotonic Stack
5	Inorder Successor in BSTPREMIUM	Easy	1378	71	DFS Traversal (Inorder, Preorder, Postorder)

+ 14 more BST Operations (Insert, Delete, Validate) problems →

Lowest Common Ancestor

13 problems →

#	PROBLEM	DIFF	ELO	IMP	PATTERNS
1	Lowest Common Ancestor of a Binary Tree	Easy	1387	87	DFS Traversal (Inorder, Preorder, Postorder)
2	Lowest Common Ancestor of a Binary Search Tree	Easy	1222	85	BST Operations (Insert, Delete, Validate)
3	Lowest Common Ancestor of a Binary Tree IVPREMIUM	Medium	1427	72	DFS Traversal (Inorder, Preorder, Postorder) · Frequency Counting / Hash Map Lookup
4	Find Distance in a Binary TreePREMIUM	Medium	1487	72	DFS Traversal (Inorder, Preorder, Postorder)
5	Lowest Common Ancestor of a Binary Tree IIPREMIUM	Medium	1580	72	DFS Traversal (Inorder, Preorder, Postorder)

+ 8 more Lowest Common Ancestor problems →

Path Sum Problems

3 problems →

#	PROBLEM	DIFF	ELO	IMP	PATTERNS
1	Path Sum III	Medium	1530	82	Prefix Sums · DFS Traversal (Inorder, Preorder, Postorder)
2	Path Sum	Easy	1107	78	DFS Traversal (Inorder, Preorder, Postorder)
3	Path Sum II	Easy	1339	72	Path Finding with Backtracking · DFS Traversal (Inorder, Preorder, Postorder)

EVERY PATTERN

Arrays & Hashing Two Pointers Stack Binary Search Sliding Window Linked List Trees Tries Backtracking Heap / Priority Queue Graphs Core DP Intervals Greedy Advanced Graphs Advanced DP Bit Manipulation Math & Geometry

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