题目描述:
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.
For example:
Given binary tree [3,9,20,null,null,15,7]
,
3 / \ 9 20 / \ 15 7
return its depth = 3.
给出一棵二叉树,求最大深度(从根开始计算)
思路:
1.对于整棵树的深度计算可以化为两步:1.求左右子孩子的深度 2.取两个孩子的最大的深度+1。从而将大问题化为局部的求解
2.时间复杂度O(n)
代码只有一行即可,极为简洁:
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/**
* 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)
{
return root==NULL ? 0 : max(maxDepth(root->left),maxDepth(root->right))+1;
}
};