import java.util.*;
/*
* public class TreeNode {
* int val = 0;
* TreeNode left = null;
* TreeNode right = null;
* }
*/
public class Solution {
/**
*
* @param root TreeNode类
* @return int整型
*/
public int maxDepth (TreeNode root) {
// write code here
if (root == null){
return 0;
}
Queue<TreeNode> queue = new LinkedList<>();
queue.add(root);
int depth = 0;
//使用层序遍历
while (!queue.isEmpty()){
int size = queue.size();
//此时queue 的容量即代表本层有多少节点
//把下层节点全部push 之后,总深度+1
for (int i = 0; i < size; i++) {
TreeNode poll = queue.poll();
if (poll.left!=null){
queue.offer(poll.left);
}
if (poll.right!=null){
queue.offer(poll.right);
}
}
depth++;
}
return depth;
}
}