If the sum between two point A and B is S. And The sum between A and C is Also S.then the Sum between two point B and C is Zero; Sum(A---------B)=S, **** Sum(A---------C)=S, **** Sum(B---------C)=0.* like {4,3,3,2,-2,3,4,-7,2} here A point is 0th-index ,B ponit is 3rd index and C point is 8th index.you can make test cases and try it.