Add possible combinations of r elements in a given array

Question

Hi Experts,

 

Add  all possible combinations of r elements in a given array of size n

Example: is input array     

int[] arr = new int[] { 1, 2, 3, 4, 5,6 };

output:  possible combination of arrary below:

1+4+5=10

2+3+5 =10
1+2+3+4=10

6+4=10
6+1+3=10

please help me

Thanks & Regards
Ashish Kumar Sahu