LeetCode 104 Maximum Depth of Binary Tree - Strategy

What is the max depth of a node? It is $1$ (for itself) plus the max depth of its tallest child.

For a leaf, the max depth is $1$ (itself). For an empty tree, the depth is $0$.

This is a recursive definition. The base case is when the node is null (depth $0$). The recursive case combines the depths of left and right children.

This pattern applies to many tree problems. Define the answer for a node in terms of the answers for its children.