ゼロから始まるLCブラシ問題(23):Maximum Depth of Binary Treeツリー深さ

原題:
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.
二叉木の深さを求めてdfsだけでよくて、各ノードは左右のサブツリーの最大値を求めてそして最大値+1を返して、結果:
Success
Runtime: 8 ms, faster than 98.23% of C++ online submissions for Maximum Depth of Binary Tree.
Memory Usage: 19.1 MB, less than 93.50% of C++ online submissions for Maximum Depth of Binary Tree.
コード:

/**
 * 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 maxDepth(TreeNode* root) {
        if (root==NULL){return 0;}
        int l=maxDepth(root->left);
        int r=maxDepth(root->right);
        if (l>=r){return l+1;}
        else return r+1;
    }
};