if the concatenation results in mask of Pandigital Concatenation , calculate all pairs formed with Masks i and j
if ( ( i j ) == pandigitalMask && freq . has ( i ) && freq . has ( j ) ) { if ( i == j ) ans += ( freq . get ( i ) * ( freq . get ( i ) - 1 ) ) ; else ans += ( freq . get ( i ) * freq . get ( j ) ) ; } } }