Let assume that ‘k’ is an integer that indicate and reveals exactly the length of subset that sum to 0. Thus length of subset to pick is determined by ‘k’. If I would like to pick only ‘k’ distinct set of integers from any given set of integers in polynomial time without having needed to check through every possible length other than the chosen length. What will be the time complexity and the size of the following examples?

Given a set of integers {-3, 17, 30, 12, -8 -15, 7, 45, 16, 9} is there a non-empty subset whose sum is zero? Yes, because k = 5. Output {-3, 17, -8, -15, 9 = 0} 
Given a set of integers {12, 5, -6, 7, -22} is there a non-empty subset whose sum is zero? No, because k = null. Output none
Given a set of integers {8, 20, 3, 35, -2, 3, 40, 7, 16, -9, 25} is there a non-empty subset whose sum is zero? Yes, because k = 4. Output {8, 3, -2, -9 = 0} 
Given a set of integers {-2, 10, 15, 20, 3, 12, 45, -6, 17, 1, 18, 5} is there a non-empty subset whose sum is zero? Yes because k = 9. Output {-2, 15, 3, 12, -45, -6, 17, 1, 5 = 0} 

Sounds suspiciously like a homework question to me. Don't expect anyone here to do it for you.