1 import java.util.ArrayList;
 2 import java.util.Stack;
 3 /*
 4 public class TreeNode {
 5     int val = 0;
 6     TreeNode left = null;
 7     TreeNode right = null;
 8 
 9     public TreeNode(int val) {
10         this.val = val;
11 
12     }
13 
14 }
15 */
16 public class Solution {
17     public ArrayList<ArrayList<Integer> > Print(TreeNode root) {
18         ArrayList<ArrayList<Integer>> res = new ArrayList<ArrayList<Integer>>();
19         Stack<TreeNode> stack1 = new Stack<TreeNode>();
20         Stack<TreeNode> stack2 = new Stack<TreeNode>();
21         int flag = 1;
22         stack1.push(root);
23         while(!stack1.empty()||!stack2.empty()){
24             if(flag==1){
25                 ArrayList<Integer> res_temp = new ArrayList<Integer>(); 
26                 while(!stack1.empty()){
27                     TreeNode resNode = stack1.pop();
28                     if(resNode !=null){
29                         res_temp.add(resNode.val);
30                         stack2.push(resNode.left);
31                         stack2.push(resNode.right);
32                     }
33                 }
34                 if(!res_temp.isEmpty())
35                     res.add(res_temp);
36                 flag = 1-flag;
37             }
38             else{
39                 ArrayList<Integer> res_temp = new ArrayList<Integer>(); 
40                 while(!stack2.empty()){
41                     TreeNode resNode = stack2.pop();
42                     if(resNode!=null){
43                         res_temp.add(resNode.val);
44                         stack1.push(resNode.right);
45                         stack1.push(resNode.left);
46                     }
47                 }
48                    if(!res_temp.isEmpty())
49                     res.add(res_temp);
50                  flag = 1-flag;
51             }
52         }
53         return res;
54     }
55 
56 }