字符串的排列

 1 import java.util.*;
 2 public class Solution {
 3     Set<String> s;
 4     public void dfs(ArrayList<String> ans, String temp, String str, boolean []vis) {
 5         if (temp.length() == str.length()) {
 6             if (!s.contains(temp)) {
 7                 ans.add(temp);
 8                 s.add(temp);
 9             }
10             return;
11         }
12         int n = str.length();
13         for (int i = 0; i < n; ++i) {
14             if (vis[i]) continue;
15             vis[i] = true;
16             dfs(ans, temp + str.substring(i, i + 1), str, vis);
17             vis[i] = false;
18         }
19     }
20     public ArrayList<String> Permutation(String str) {
21         int n = str.length();
22         ArrayList<String> ans = new ArrayList<>();
23         if (n == 0) return ans;
24         s = new HashSet<>();
25         boolean []vis = new boolean [n + 1];
26         String temp = new String();
27         dfs(ans, temp, str, vis);
28         return ans;
29     }
30 }