LeetCode Generate Parentheses

 1 public class Solution {
 2     String parenthes = "()";
 3     List<String> lastParenthesis=new ArrayList<>();
 4     public List<String> generateParenthesis(int n) {
 5             List<String> Parenthesis=new ArrayList<>();
 6         if (n==0) {
 7             return lastParenthesis;
 8         }
 9         lastParenthesis.add(parenthes);
10         if (n==1) {    
11             return lastParenthesis;
12         }else {
13             for (int i = 2; i <=n; i++) {
14                 for (String eleP : lastParenthesis) {
15                     for (int j = 0; j < eleP.length(); j++) {
16                         String newone=eleP.substring(0, j+1)+parenthes+eleP.substring(j+1);
17                         if (!Parenthesis.contains(newone)) {
18                             Parenthesis.add(newone);
19                         }
20                     }
21 
22                 }
23                     lastParenthesis.clear();
24                     lastParenthesis.addAll(Parenthesis);
25                     Parenthesis.clear();
26             }
27         }
28         return lastParenthesis;
29     }
30 }