leetcode刷题笔记(Golang)--60. Permutation Sequence

60. Permutation Sequence

The set [1,2,3,…,n] contains a total of n! unique permutations.

By listing and labeling all of the permutations in order, we get the following sequence for n = 3:

“123”
“132”
“213”
“231”
“312”
“321”
Given n and k, return the kth permutation sequence.

Note:

Given n will be between 1 and 9 inclusive.
Given k will be between 1 and n! inclusive.
Example 1:

Input: n = 3, k = 3
Output: “213”
Example 2:

Input: n = 4, k = 9
Output: “2314”

基于数学运算的解题思路

	factors := make([]int, 10, 10)
	nums := make([]int, 9, 9)
	res := ""
	factors[0] = 1
	nums[0] = 1
	for i := 1; i < 9; i++ {
		factors[i] = factors[i-1] * i
		nums[i] = i + 1
	}
	k--
	for i := n; i >= 1; i-- {
		rs := k / factors[i-1]
		fmt.Println(nums[rs], reflect.TypeOf(string(nums[rs])))
		k %= factors[i-1]
		res += string(nums[rs] + '0')
		nums = append(nums[:rs], nums[rs+1:]...)
	}
	return res