Permutation Sequence

 1 public class Solution {
 2     public String getPermutation(int n, int k) {
 3         int num[] = new int [n];
 4         int permu = 1;
 5         for(int i=0;i<n;i++){
 6             num[i]=i+1;
 7             permu *= i+1;
 8         }
 9         k--;        
10         StringBuilder sb =new StringBuilder();
11         for(int i=0;i<n;i++){
12             permu /=n-i;
13             int selected = k/permu;
14             sb.append(num[selected]);
15             k %= permu;
16             for(int j=selected+1;j<n;j++){
17                 num[j-1] = num[j];
18             }
19         }
20         return sb.toString();
21     }
22 }