559. N叉树的最大深度

/*
// Definition for a Node.
class Node {
    public int val;
    public List<Node> children;

    public Node() {}

    public Node(int _val) {
        val = _val;
    }

    public Node(int _val, List<Node> _children) {
        val = _val;
        children = _children;
    }
};
*/

/*
// Definition for a Node.
class Node {
    public int val;
    public List<Node> children;

    public Node() {}

    public Node(int _val) {
        val = _val;
    }

    public Node(int _val, List<Node> _children) {
        val = _val;
        children = _children;
    }
};
*/

class Solution {
    public int maxDepth(Node root) {
        if(root == null) {
            return 0;
        } else if (root.children.isEmpty()) {
            return 1;
        } else {
            List<Integer> list = new LinkedList<>();
            //此处children是root的一个list属性，可用增强for遍历
            for(Node node : root.children) {    //将所有子树全部递归
                list.add(maxDepth(node));   //所有子树的最大深度添加到list中
            }
            return Collections.max(list) + 1;    //后边加1是加根节点高度
        }
    }
}

collections.max()用法

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