剑指offer-22

import java.util.ArrayList;
import java.util.Queue;
import java.util.LinkedList;

public class Solution {
    public ArrayList<Integer> PrintFromTopToBottom(TreeNode root) {
        ArrayList<Integer> list = new ArrayList();
        Queue<TreeNode> queue = new LinkedList();
        if(root == null){
            return list;
        }
        queue.offer(root);
        while(!queue.isEmpty()){
            TreeNode treeNode = queue.poll();
            list.add(treeNode.val);
            if(treeNode.left != null){
                queue.offer(treeNode.left);
            }
            if(treeNode.right != null){
                queue.offer(treeNode.right);
            }
        }
        return list;
    }
}