Trees & BST
Hierarchical structures — traversals, path problems, LCA, and balanced BST operations
0/50 solved
Tree Traversals (BFS/DFS)
Master inorder, preorder, postorder, and level-order to unlock all tree problems
Approach
BFS: Use a queue, process level by level. DFS: Use recursion or stack. Inorder (left-root-right) gives sorted order for BST. Preorder (root-left-right) for tree serialization. Postorder (left-right-root) for deletion and evaluation.
How to Recognize
Problem asks to visit nodes in a specific order
Need level-by-level processing (BFS) or depth-first exploration (DFS)
Phrases like 'zigzag level order', 'right side view', 'boundary traversal'
Need to collect nodes at specific depths or in specific sequences
Pro Tips
BFS uses a Queue; DFS uses recursion or an explicit Stack
For zigzag, alternate the direction of insertion at each level
Iterative inorder using a stack is the foundation for BST iterator design
10
Total
6
Easy
4
Medium
0
Hard
Time
O(n)
Space
O(n)