从上往下打印二叉树

题目描述

从上往下打印出二叉树的每个节点，同层节点从左至右打印。

import java.util.ArrayList;

/*
 * 题目描述
 * 从上往下打印出二叉树的每个节点，同层节点从左至右打印。
 */

public class Main22 {

    public static void main(String[] args) {
        // TODO Auto-generated method stub

    }
    
    public class TreeNode {
        int val = 0;
        TreeNode left = null;
        TreeNode right = null;

        public TreeNode(int val) {
            this.val = val;
        }
    }
    
    public ArrayList<Integer> PrintFromTopToBottom(TreeNode root) {
        ArrayList<Integer> array = new ArrayList<Integer>();
        ArrayList<TreeNode> treeArray = new ArrayList<TreeNode>();
        if (root == null) {
            return array;
        }
        treeArray.add(root);
        for (int i=0;i<treeArray.size();i++) {
            TreeNode head = treeArray.get(i);
            if (head.left != null) {
                treeArray.add(head.left);
            }
            if (head.right != null) {
                treeArray.add(head.right);
            }
            array.add(head.val);
        }
        return array;
    }

}