LeetCode Online Judge 题目C# 练习 - 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 (ie, 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.

 1         public static string PermutationSequence(int n, int k)

 2         {

 3             List<int> num = new List<int>();

 4             for (int i = 1; i <= n; i++)

 5             {

 6                 num.Add(i);

 7             }

 8 

 9             for (int i = 1; i < k; i++)

10             {

11                 NextPermutation(num);

12             }

13 

14             string ret = "";

15             foreach (var item in num)

16             {

17                 ret += Convert.ToString(item);

18             }

19 

20             return ret;

21         }

代码分析：

　　如果做了之前的一题， Next Permutation，这一题就是吃菜了。