algorithm - 模式匹配列表尾元组元素

Question

我有一些作为练习编写的运行长度编码代码

let rle s = 
    s
    |> List.map (fun x -> (x, 1))
    |> List.fold (fun acc x -> 
        match acc with 
            | [] -> [(x, 1)]
            | h::(x, n) -> h::(x, n+1)
            | h -> h::(x, 1)
        )
    |> List.map (fun (x, n) -> 
        match n with
            | 1 -> x.ToString()
            | _ -> x.ToString() + n.ToString()
        )

模式 h::(x, n) -> h::(x, n+1) 编译失败。

有人知道为什么吗？

Answer 1

RLE(笑脸)

let rle (s: string) = 
  let bldr = System.Text.StringBuilder()
  let rec start = function
    | [] -> ()
    | c :: s -> count (1, c) s
  and count (n, c) = function
    | c1 :: s when c1 = c -> count (n+1, c) s
    | s -> Printf.bprintf bldr "%d%c" n c; start s
  start (List.ofSeq s)
  bldr.ToString()

let s1 = "WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW"
let s2 = "12W1B12W3B24W1B14W"

rle s1 = s2 |> printfn "%b" //"true"