Given two integers N and K. Find the kth permutation sequence of first N natural numbers.

Example 1:
Input: 4 3
Output: 1324
Explanation:
Permutations of first 4 natural numbers:
1234,1243,1324,1342,1423,1432.....
So the 3rd permutation is 1324.
Example 2:
Input: 3 5
Output: 312
Explanation:
Permutations of first 3 natural numbers:
123,132,213,231,312,321.
So the 5th permutation is 312.
Your Task:
You don't need to read input or print anything. Your task is to complete the function kthPermutation() which takes two integers N and K as input parameters and returns an string denoting the kth permutation.
Expected Time Complexity: O(N)
Expected Auxiliary Space: O(N)
Constraints:
1 <= N <= 9
1 <= K <= N!

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