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。