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.
题意:给定一个二叉树,返回最大深度
思路:这里也是用了BFS,只是用depth来记录深度,每遍历一层,深度加1
class Solution { public: //迭代,BFS,自顶向下,利用队列 int maxDepth(TreeNode* root) { if(root==NULL) return 0; int depth=0; queue<TreeNode *> q; q.push(root); while(!q.empty()){ depth++; int n=q.size(); for(int i=0;i<n;i++){ TreeNode * t=q.front(); q.pop(); if(t->left) q.push(t->left); if(t->right) q.push(t->right); } } return depth; } };