LeetCode: Permutation Sequence

这题的难度在编程，一开始想到的dfs过不了large，第二次想到网上的正确答案的思路，不过没有编出来，然后只好找答案了

 1 class Solution {

 2 public:

 3     string getPermutation(int n, int k) {

 4         // Start typing your C/C++ solution below

 5         // DO NOT write int main() function

 6         string ret = "";

 7         int time = 1;

 8         for (int i = 1; i <= n; i++) {

 9             ret += (char)('0'+i);

10             time *= i;

11         }

12         k--;

13         k %= time;

14         time /= n;

15         for (int i = 0; i < n-1; i++) {

16             int select = k / time;

17             k %= time;

18             time /= n - i - 1;

19             int tmp = ret[i + select];

20             for (int j = select; j > 0; j--) ret[i+j] = ret[i+j-1];

21             ret[i] = tmp;

22         }

23         return ret;

24     }

25 };