Permutation Sequence

    string getPermutation(int n, int k) {
        string num, res;
        int total = 1;
        for (int i = 1; i <= n; ++i)
        {
            num.push_back(i + '0');
            total *= i;
        }
        k--;
        while (n)
        {
            total /= n;
            int i = k / total;
            k %= total;
            res.push_back(num[i]);
            num.erase(i, 1);
            n--;
        }
        return res;
    }