根节点的深度 = max(左子树深度,右子树深度)+ 1
注意特殊情况:只有头节点的空树
/**
* Definition for a binary tree node.
* struct TreeNode {
* int val;
* TreeNode *left;
* TreeNode *right;
* TreeNode(int x) : val(x), left(NULL), right(NULL) {}
* };
*/
class Solution {
public:
int treeDepth(TreeNode* root) {
if (root == NULL) return 0;
return max(treeDepth(root->left), treeDepth(root->right)) + 1;
}
};