text: Function to count quadruples of the required type
code: function countSubsequence ( a , n ) { let i , j ; fill_counts ( a , n ) ; let answer = 0 ; for ( i = 1 ; i < n ; i ++ ) { for ( j = i + 1 ; j < n - 1 ; j ++ ) { answer += lcount [ a [ j ] ] [ i - 1 ] * rcount [ a [ i ] ] [ j + 1 ] ; } } return answer ; }