package leetcode;
/*Given a binary tree, return the postorder traversal of its nodes' values.
*/
import java.util.ArrayList;
public class Binary_tree_postorder_traversal {
public static void main(String[] args) {
}
public ArrayList<Integer> postorderTraversal(TreeNode root) {
ArrayList<Integer> al = new ArrayList<>();
if(root == null)
return al;
al.addAll(postorderTraversal(root.left)); //注意addAll的用法,即便每次递归新建立al但是addall按照指定collection迭代器所返回的元素顺序,追加到列表末尾
al.addAll(postorderTraversal(root.right));
al.add(root.val);
return al;
}
}