【剑指Offer】32.3 按之字形顺序打印二叉树

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 {
    public ArrayList<ArrayList<Integer>> Print(TreeNode pRoot) {
        ArrayList<ArrayList<Integer>>  ret = new ArrayList<>();
        Queue<TreeNode> queue = new LinkedList<>();
        Boolean re = false;
        queue.add(pRoot);
        
        while(!queue.isEmpty()) {
            int len = queue.size();
            ArrayList<Integer> list = new ArrayList<>();
            while(len-- > 0) {
                TreeNode node = queue.poll();
                if(node == null)
                    continue;
                list.add(node.val);
                queue.add(node.left);
                queue.add(node.right);
            }
            if(re == true) {
                Collections.reverse(list);
            }
            re = !re;
            if(list.size() != 0)
                ret.add(list);
        }
        return ret;
    }
}