public class Solution {
public List<Integer> postorder(Node root) {
List<Integer> res = new ArrayList<>();
helper(root, res);
return res;
}
private void helper(Node root, List<Integer> res) {
if (root != null) {
if (root.children != null)
for (int i = 0; i < root.children.size(); i++)
helper(root.children.get(i), res);
res.add(root.val);
}
}
}迭代没看懂。。。