Question

这是我必须制作回文功能的代码。我之前已经创建了listReverse和explode函数来制作回文。有人可以帮我修复回文功能吗？

let rec listReverse l = match l with
    |[] -> []
    |head :: tail -> (listReverse tail) @ [head]



    (* explode : string -> char list 
     * (explode s) is the list of characters in the string s in the order in 
     *   which they appear
     * e.g.  (explode "Hello") is ['H';'e';'l';'l';'o']
     *)
    let explode s = 
      let rec _exp i = 
        if i >= String.length s then [] else (s.[i])::(_exp (i+1)) in
      _exp 0


    let rec palindrome w = 
    let a = explode w in
    let b = listReverse a in
    if c :: d 
    else false

Answer 1

您应该使用List.rev标准功能来反转列表。 Ocaml是一个免费软件，你应该看看它的实现（文件stdlib/list.ml）

Answer 2

尝试用简单的英语（而不是代码）解释你在写作时想要达到的目标

if c :: d 
  else false

另外，请注意

if foo = bar then true else false

应该简化为

foo = bar

Answer 3

您可以将if语句替换为：

 (* tells wheter its a palindrome or not; most is (List.length a)/2*)
 let rec same l1 l2 cur most =
     match l1, l2 with
         | h1::t1, h2::t2 when h1 = h2 -> 
             if cur < most then same t1 t2 (cur+1) most
             else true
         | _ -> false in

 same a b 0 ((List.length a)/2)

ocaml list反向错误

3 个答案: