letecode [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.

题目大意：

　　给定一个二叉树，计算二叉树的深度

理解：

　　根节点为空，深度为0；根节点左右子树为空，深度为1。

　　每递归一层深度+1.

代码C++：

 

/**
 * 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;
        if(root->left==NULL && root->right==NULL) return 1;
        int left = maxDepth(root->left);
        int right = maxDepth(root->right);
        return left>right?left+1:right+1;
    }
};

 

运行结果：

　　执行用时 : 12 ms　　内存消耗 : 19.3 MB