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.

public static string PermutationSequence(int n, int k)
{
List<int> num = new List<int>();
for (int i = 1; i <= n; i++)
{
num.Add(i);
}

for (int i = 1; i < k; i++)
{
NextPermutation(num);
}

string ret = "";
foreach (var item in num)
{
ret += Convert.ToString(item);
}

return ret;
}

代码分析：

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