按之字形顺序打印二叉树

class Solution{ public class TreeNode { int val = 0; TreeNode left = null; TreeNode right = null; public TreeNode(int val) { this.val = val; } } public ArrayList<ArrayList<Integer> > Print(TreeNode pRoot) { ArrayList<ArrayList<Integer>> result = new ArrayList<ArrayList<Integer>>(); if(pRoot==null)//边界条件 return result; ArrayList<TreeNode> ele = new ArrayList<TreeNode>();//保存每一层的树节点 ele.add(pRoot); boolean flag = true;//标记位 while(!ele.isEmpty()){ ArrayList<Integer> temp = new ArrayList<Integer>();//每一层树节点的值 int len = ele.size(); for(int i = 0;i<len;i++){ TreeNode node = ele.get(0); if(node.left!=null) ele.add(node.left); if(node.right!=null) ele.add(node.right); if(flag) temp.add(node.val);//尾部追加类似于队列 else temp.add(0,node.val);//从头部添加，类似于栈 ele.remove(0); } flag ^=true;//改变放入方向 result.add(temp); } return result; } }