Subsequence of length 4 of type 1 2 1 2
for ( i = 0 ; i < n ; i ++ ) { for ( j = i + 1 ; j < n ; j ++ ) { if ( a [ i ] == 1 && a [ j ] == 1 && ( suff [ i ] - suff [ j ] ) >= 1 && suff [ j ] >= 1 ) { ss += ( suff [ i ] - suff [ j ] ) * suff [ j ] ; } } } cout << ( ss ) ; }