leetcode-com-explore-challenge-card-june-leetcoding-challenge-541-week-3-june-15th-june-21st-3366.cpp

class Solution {
public:
    string getPermutation(int n, int k) {
        string res;
        string nums = "123456789";
        int f[10] = {1, 1, 2, 6, 24, 120, 720, 5040, 40320, 362880};
        --k;
        for (int i = n; i >= 1; --i) {
            int j = k / f[i - 1];
            k %= f[i - 1];
            res.push_back(nums[j]);
            nums.erase(nums.begin() + j);
        }
        return res;
    }
};