Input: n = 3, k = 2 Output: 3 Explanation: Let the set be {1, 2, 3}, we can partition it into 2 subsets in following ways {{1,2}, {3}}, {{1}, {2,3}}, {{1,3}, {2}} Input: n = 3, k = 1 Output: 1 Explanation: There is only one way {{1, 2, 3}}