change value of Array elements at fix location as per rule ( n * n + 1 ) - arr [ i ] [ j ] Top Left corner of Matrix ( order ( n / 4 ) * ( n / 4 ) )
for ( i = 0 ; i < n / 4 ; i ++ ) for ( j = 0 ; j < n / 4 ; j ++ ) arr [ i ] [ j ] = ( n * n + 1 ) - arr [ i ] [ j ] ;