Recursion method:
/*
// 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 {
List<Integer> res = new ArrayList();
public List<Integer> preorder(Node root) {
dns(root);
return res;
}
public void dns(Node node){
if(node == null){
return;
}
res.add(node.val);
List<Node> nodeList = node.children;
if(nodeList == null){
return;
}
for(int i = 0;i < nodeList.size();i++){
dns(nodeList.get(i));
}
}
}