leetcode讲解–559. Maximum Depth of N-ary Tree

题目
Given a n-ary 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 a 3-ary tree:

We should return its max depth, which is 3.
Note:

The depth of the tree is at most 1000.
The total number of nodes is at most 5000.

题目地址
讲解
这道题需要对每次层的深度做个记录，我直接使用结点的val属性来记录深度。另外就是给根节点深度置为1的时候有个技巧，设置一个一次性的flag。
Java代码
/*
// Definition for a Node.
class Node {
public int val;
public List<Node> children;

public Node() {}

public Node(int _val,List<Node> _children) {
val = _val;
children = _children;
}
};
*/
class Solution {
private int result=0;
private boolean flag = true;
public int maxDepth(Node root) {
if(root==null){
return result;
}
if(flag){
root.val=1;
flag = false;
}
if(result<root.val){
result = root.val;
}
for(Node node:root.children){
node.val = root.val+1;
maxDepth(node);
}
return result;
}

}