相关疑难解决方法(0)

我必须对列表列表进行投影,这些列表返回每个列表中每个元素的所有组合.例如:

projection([[1]; [2; 3]]) = [[1; 2]; [1; 3]].
projection([[1]; [2; 3]; [4; 5]]) = [[1; 2; 4]; [1; 2; 5]; [1; 3; 4]; [1; 3; 5]].

我想出了一个功能:

let projection lss0 =
    let rec projectionUtil lss accs =
        match lss with
        | []        ->  accs
        | ls::lss'  ->  projectionUtil lss' (List.fold (fun accs' l -> 
                                                        accs' @ List.map (fun acc -> acc @ [l]) accs) 
                                                        [] ls)
match lss0 with
| [] -> []
| ls::lss' ->         
    projectionUtil lss' (List.map …