19.3.5 [LeetCode 104] Maximum Depth of Binary Tree

Given a binary tree, find its maximum depth.

The maximum depth is the number of nodes along the longest path from the root node down to the farthest leaf node.

Note: A leaf is a node with no children.

Example:

Given binary tree [3,9,20,null,null,15,7],

    3
   / 
  9  20
    /  
   15   7

return its depth = 3.

class Solution {
public:
    int maxDepth(TreeNode* root) {
        if(!root)return 0;
        return max(1+maxDepth(root->left),1+maxDepth(root->right));
    }
};