UVA - 11063 - B2-sequence

problem statement

Simulation - STL - set
complete search

take care about negative numbers
take care about repetitive numbers
take care about this numbers have to be in increasing order
1 <= b1 < b2 < b3 ...

            if( a[i] <= 0 )
                isB2 = false;

            if( i >= 1 && a[i] <= a[i-1] )
                isB2 = false;

                if( mark.count( a[i]+a[j] ) == true )
                    isB2 = false;