按之字形打印二叉树

题目描述

请实现一个函数按照之字形打印二叉树，即第一行按照从左到右的顺序打印，第二层按照从右至左的顺序打印，第三行按照从左到右的顺序打印，其他行以此类推。

 1 import java.util.ArrayList;
 2 import java.util.Stack;
 3 
 4 /*
 5 public class TreeNode {
 6     int val = 0;
 7     TreeNode left = null;
 8     TreeNode right = null;
 9 
10     public TreeNode(int val) {
11         this.val = val;
12 
13     }
14 
15 }
16 */
17 public class Solution {
18     public ArrayList<ArrayList<Integer> > Print(TreeNode pRoot) {
19         
20         Stack<TreeNode> []level = new Stack[2];
21         level[0] = new Stack<TreeNode>();
22         level[1] = new Stack<TreeNode>();
23         ArrayList<ArrayList<Integer>> ans = new ArrayList<>();
24         if (pRoot == null) return ans;
25         level[0].push(pRoot);
26         int now = 0;
27         ArrayList<Integer> l = new ArrayList<>();
28         int num = 0;
29         while (!level[0].empty() || !level[1].empty()) {
30             TreeNode temp = level[now].pop();
31             l.add(temp.val);
32             int next = (now + 1) % 2;
33             if (num % 2 == 0) {
34                 if (temp.left != null) {
35                     level[next].push(temp.left);
36                 }
37                 if (temp.right != null){
38                     level[next].push(temp.right);
39                 }
40                 
41             } else {
42                 if (temp.right != null){
43                     level[next].push(temp.right);
44                 }
45                 if (temp.left != null) {
46                     level[next].push(temp.left);
47                 }
48                 
49             }
50             if (level[now].empty()) {
51                 now = (now + 1) % 2;
52                 num++;
53                 ans.add(new ArrayList<Integer>(l));
54                 l = new ArrayList<>();
55             }
56             
57             
58         }
59         return ans;
60     }
61 
62 }