从上往下打印二叉树java实现

import java.util.ArrayList;
import java.util.Deque;
import java.util.LinkedList;
/**
public class TreeNode {
int val = 0;
TreeNode left = null;
TreeNode right = null;

public TreeNode(int val) {
this.val = val;

}

}
*/
public class Solution {
public ArrayList<Integer> PrintFromTopToBottom(TreeNode root) {
ArrayList<Integer> list = new ArrayList<Integer>();
if(root == null) return list;
Deque<TreeNode> deque = new LinkedList<TreeNode>();

deque.add(root);
while(!deque.isEmpty()){
TreeNode t = deque.pop();
list.add(t.val);
if(t.left != null) deque.add(t.left);
if(t.right != null) deque.add(t.right);
}
return list;
}
}