Return the top k elements of an input vector. A comparison function compareFcn(m,n) is provided to compare individual elements of the vector. The function returns true is element m should be ranked higher than element n. e.g.

partial_sort([4 3 2 1], 2, @(m,n) m > n)

ans =

       4     3

partial_sort([4 3 2 1], 2, @(m,n) m < n)

ans =

       1     2

All elements in the input vector will be unique.

Solutions will be ranked on the total number of times comparison functions are called, over all the test cases.