Create 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): 
1."123"
2."132"
3."213"
4."231"
5."312"
6."321"


Given n and k, return the kth permutation sequence.

Note: Given n will be between 1 and 9 inclusive.