面试题32：从上到下打印二叉树

层次遍历二叉树

import java.util.ArrayList;
 
import java.util.List;
import java.util.Queue;
import java.util.concurrent.LinkedBlockingDeque;
/**
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) {
        List<Integer> list = new ArrayList<Integer>();
         if(root==null)
            return (ArrayList<Integer>) list;
        Queue<TreeNode> queue = new LinkedBlockingDeque<TreeNode>();
        queue.add(root);
        while(queue.size()>0){
            TreeNode node05 = queue.poll();
            list.add(node05.val);
            if(node05.left!=null)
                queue.add(node05.left);
            if(node05.right!=null)
                queue.add(node05.right);
        }
        return (ArrayList<Integer>) list;
    }
}