OCaml处理Advent of Code 2022输入时触发Invalid_argument错误求助

你的错误来自read_lines函数返回的列表中包含空字符串。当文件末尾存在换行符时，String.split_on_char '\n'会把最后一个换行后的空内容也加入列表（比如你的input.txt最后一行可能带换行，导致列表变成["A X"; "B Y"; "C Z"; ""]）。而scorer函数调用String.sub s 0 1和String.sub s 2 1时，空字符串的长度不足以支持这些操作，直接触发Invalid_argument异常。手动定义lines时不会包含空串，所以能正常运行。

修改read_lines函数，过滤掉拆分后产生的空字符串：

let read_lines filename =
  let contents = In_channel.with_open_bin filename In_channel.input_all in
  contents
  |> String.split_on_char '\n'
  |> List.filter (fun s -> String.trim s <> "")  (* 过滤空行，包括仅含空白的行 *)

如果确定输入行格式固定为3字符长度，也可以直接按长度过滤：

let read_lines filename =
  let contents = In_channel.with_open_bin filename In_channel.input_all in
  contents
  |> String.split_on_char '\n'
  |> List.filter (fun s -> String.length s >= 3)

可以在scorer函数里增加输入合法性检查，避免异常崩溃：

let scorer s =
  if String.length s < 3 then 0  (* 或者抛出更明确的错误提示 *)
  else
    let theirs =
      match String.sub s 0 1 with
      | "A" -> "X"
      | "B" -> "Y"
      | "C" -> "Z"
      | _ -> assert false
    in
    let ours = String.sub s 2 1 in
    let played =
      match ours with "X" -> 1 | "Y" -> 2 | "Z" -> 3 | _ -> assert false
    in
    let result =
      match (theirs, ours) with
      | "X", "Y" | "Y", "Z" | "Z", "X" -> 6
      | theirs, ours when theirs = ours -> 3
      | _ -> 0
    in
    played + result

内容的提问来源于stack exchange，提问作者bennouli