Function to find prefix - count for each row from right to left
function findPrefixCount ( p_arr , set_bit ) { for ( let i = 0 ; i < n ; i ++ ) { for ( let j = n - 1 ; j >= 0 ; j -- ) { if ( set_bit [ i ] [ j ] ) continue ; if ( j != n - 1 ) p_arr [ i ] [ j ] += p_arr [ i ] [ j + 1 ] ; p_arr [ i ] [ j ] += ( ! set_bit [ i ] [ j ] ) ? 1 : 0 ; } } } class pair { constructor ( a , b ) { this . first = a ; this . second = b ; } }