1079. 活字印刷

 1 public class Solution {
 2     private char[] titles = null;
 3     private int count = 0;
 4     private boolean[] flag = null;
 5     private int len = -1;
 6 
 7     private void helper(){
 8 
 9         for (int i = 0; i < len; i++) {
10             if (!flag[i]){
11                 ++count;
12                 flag[i] = true;
13                 helper();
14                 flag[i] = false;
15                 while (i+1<len && titles[i] == titles[i+1]) ++i;
16             }
17         }
18     }
19 
20     public int numTilePossibilities(String tiles) {
21         this.titles = tiles.toCharArray();
22         len = tiles.length();
23         flag = new boolean[len];
24         Arrays.sort(this.titles);
25         helper();
26         return count;
27     }
28 
29     public static void main(String[] args) {
30         int aa = new Solution().numTilePossibilities("AAAB");
31         System.out.println("aa = " + aa);
32     }
33 }