Verify Preorder Serialization of a Binary Tree

 1 public class Solution {
 2     public boolean isValidSerialization(String preorder) {
 3         String[] nodes = preorder.split(",");
 4         int tree = 0;
 5         int leaves = 0;
 6         for (int i = nodes.length - 1; i >= 0; i--) {
 7             if (!nodes[i].equals("#")) {
 8                 tree++;
 9             } else {
10                 leaves++;
11             }
12             
13             if (leaves - tree < 1) {
14                 return false;
15             }
16         }
17         return leaves - tree == 1;
18     }
19 }

1. This is counting leaves and trees method. It should starting from end, which gareentee the leaves is larger than tree.

A nice regex work:

1 public class Solution {
2     public boolean isValidSerialization(String preorder) {
3         String s = preorder.replaceAll("\\d+,#,#", "#");
4         return s.equals("#") || !s.equals(preorder) && isValidSerialization(s);
5     }
6 }

posted on 2016-07-01 15:56 keepshuatishuati 阅读(155) 评论(0) 编辑收藏举报