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

class Solution {
public:
    string getPermutation(int n, int k) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        string ret = "";
        int time = 1;
        for (int i = 1; i <= n; i++) {
            ret += (char)('0'+i);
            time *= i;
        }
        k--;
        k %= time;
        time /= n;
        for (int i = 0; i < n-1; i++) {
            int select = k / time;
            k %= time;
            time /= n - i - 1;
            int tmp = ret[i + select];
            for (int j = select; j > 0; j--) ret[i+j] = ret[i+j-1];
            ret[i] = tmp;
        }
        return ret;
    }
};