【剑指Offer】32.2 把二叉树打印成多行

import java.util.*;


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

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

    }

}
*/
public class Solution {
    ArrayList<ArrayList<Integer> > Print(TreeNode pRoot) {
        ArrayList<ArrayList<Integer>> ret = new ArrayList<>();
        Queue<TreeNode> queue = new LinkedList<>();
        queue.add(pRoot);
        while(!queue.isEmpty()) {
            ArrayList<Integer> list = new ArrayList<>();
            int len = queue.size();
            while(len-- > 0) {
                TreeNode node = queue.poll();
                if(node == null)
                    continue;
                list.add(node.val);
                queue.add(node.left);
                queue.add(node.right);
            }
            if(list.size() != 0)
                ret.add(list);
        }
        return ret;
    }
}