Cheat Sheet

Trees Cheat Sheet

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What is Trees?

Traverse and manipulate hierarchical data structures.

Trigger Words

When you see these in a problem, think Trees:

invert binary tree trees maximum depth of binary tree validate binary search tree lowest common ancestor of a binary search tree binary tree level order traversal binary tree right side view serialize and deserialize binary tree binary tree maximum path sum

Template Code

def invertTree(root: TreeNode) -> TreeNode:
    if not root:
        return None
    
    # Swap left and right children
    root.left, root.right = root.right, root.left
    
    # Recursively invert subtrees
    invertTree(root.left)
    invertTree(root.right)
    
    return root

Complexity

Typical Time	`O(n)`
Typical Space	`O(h)`

Common Variations

Basic Trees
Trees with constraints
Optimized Trees

Practice Problems

Invert Binary Tree medium Maximum Depth of Binary Tree medium Validate Binary Search Tree medium Lowest Common Ancestor of a Binary Search Tree medium Binary Tree Level Order Traversal medium

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Practice Trees

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