Maximum Size Subset with Given Sum

we need to find size of maximum size subset whose sum is equal to given sum.

Input : set[] = {2, 3, 5, 7, 10, 15},
         sum  = 10
Output : 3
The largest sized subset with sum 10
is {2, 3, 5}

Input : set[] = {1, 2, 3, 4, 5}
         sum = 4
Output : 2