leetcode -- Permutation Sequence

The set [1,2,3,…,n] contains a total of n! unique permutations.

By listing and labeling all of the permutations in order,
We get the following sequence (ie, for n = 3):

  1. "123"
  2. "132"
  3. "213"
  4. "231"
  5. "312"
  6. "321"

 Given n and k, return the kth permutation sequence.

Note: Given n will be between 1 and 9 inclusive.

 1 public class Solution {
 2     public String getPermutation(int n, int k) {
 3         // Start typing your Java solution below
 4         // DO NOT write main() function
 5         int[] num = new int[n];
 6         int count = 1;
 7         for(int i = 0; i < n; i++){
 8             num[i] = i + 1;
 9             count *= (i+1);
10         }
11         k--;
12         StringBuilder sb = new StringBuilder();
13         for(int i = 0; i < n; i++){
14             count /= n - i;
15             int selected = k / count;
16             k = k % count;
17             //count = count / (n - i - 1);
18             
19             sb.append(num[selected]);
20             for(int j = selected + 1; j < n; j++){
21                 num[j - 1] = num[j];
22             }
23         }
24         return sb.toString();
25     }
26 }

 

 

posted @ 2013-08-11 13:13  feiling  阅读(586)  评论(0)  编辑  收藏  举报