题目：

题解：

func getPermutation(n int, k int) string {factorial := make([]int, n)factorial[0] = 1for i := 1; i < n; i++ {factorial[i] = factorial[i - 1] * i}k--ans := ""valid := make([]int, n + 1)for i := 0; i < len(valid); i++ {valid[i] = 1}for i := 1; i <= n; i++ {order := k / factorial[n - i] + 1for j := 1; j <= n; j++ {order -= valid[j]if order == 0 {ans += strconv.Itoa(j)valid[j] = 0break}}k %= factorial[n - i]}return ans
}