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この問題は、機械式走行距離計のすべての可能な読み取り値を見つけることと説明できますが、その車輪の桁数はさまざまである可​​能性があることに注意してください。

odometer = [["a1","a2","a3"],["b1","b2"],["c1","c2","c3","c4"]]

私がこれまでに持っているもの：

read_heads :: [[[Char]]] -> [[Char]]
read_heads [[[]]] = [[]]
read_heads x = map head x

-- pushes the first element of a list to the end
rotate :: [a] -> [a]
rotate [] = []
rotate (x:xs) = xs ++ [x]

http://www.cartell.ie/car_check/wp-content/uploads/2010/02/Odometer-1.jpg

編集：質問を明確にします。上記の走行距離計を使用して、考えられるすべての測定値を含むリストを作成します。

["a1","b1","c1"]
["a1","b1","c2"]
["a1","b1","c3"]
["a1","b1","c4"]
["a1","b2","c1"]
["a1","b2","c2"]
["a1","b2","c3"]
["a1","b2","c4"]
etc.
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1 に答える 1

7

これはおそらく最も簡単なものです：

Prelude> let odometer a = sequence a
Prelude> odometer [["a1","a2","a3"],["b1","b2"],["c1","c2","c3","c4"]]
[["a1","b1","c1"],["a1","b1","c2"],["a1","b1","c3"],["a1","b1","c4"],["a1","b2","c1"],
["a1","b2","c2"],["a1","b2","c3"],["a1","b2","c4"],["a2","b1","c1"],["a2","b1","c2"],
["a2","b1","c3"],["a2","b1","c4"],["a2","b2","c1"],["a2","b2","c2"],["a2","b2","c3"],
["a2","b2","c4"],["a3","b1","c1"],["a3","b1","c2"],["a3","b1","c3"],["a3","b1","c4"],
["a3","b2","c1"],["a3","b2","c2"],["a3","b2","c3"],["a3","b2","c4"]]
Prelude>

sequenceモナドを扱う関数です。Haskell を使いたい場合は、モナドを理解する必要があるので、今すぐ始めたほうがよいかもしれません。

強力なモナドをまだ生活に取り入れる準備ができていない場合は、より平凡なバージョンを次に示します。

Prelude> :{
Prelude| let odometer (xs:yys) = [x:ys | x<-xs, ys<-odometer yys]
Prelude|     odometer [] = [[]]
Prelude| :}
Prelude> odometer [["a1","a2","a3"],["b1","b2"],["c1","c2","c3","c4"]]
[["a1","b1","c1"],["a1","b1","c2"],["a1","b1","c3"],["a1","b1","c4"],["a1","b2","c1"],
["a1","b2","c2"],["a1","b2","c3"],["a1","b2","c4"],["a2","b1","c1"],["a2","b1","c2"],
["a2","b1","c3"],["a2","b1","c4"],["a2","b2","c1"],["a2","b2","c2"],["a2","b2","c3"],
["a2","b2","c4"],["a3","b1","c1"],["a3","b1","c2"],["a3","b1","c3"],["a3","b1","c4"],
["a3","b2","c1"],["a3","b2","c2"],["a3","b2","c3"],["a3","b2","c4"]]
Prelude>

それは缶に書かれていることを正確に行います：

  • 走行距離計ホイールのリストが与えられた場合(xs:yys)
  • 可能なすべての読み取り値のリストは、xとysの可能なすべての組み合わせのリストです。 = [ x:ys
  • そのような|
  • xは、最初のホイールのすべての可能な位置のリストから取得されますx<-xs
  • と,
  • ysは、残りの車輪 (つまり、最初の車輪以外のすべて) から作成された走行距離計のすべての可能な読み取り値のリストから取得されます ys<-odometer yys]。
  • 走行距離計に車輪がない場合[]
  • 空である可能性のある読み取りは 1 つだけです。= [[]]
于 2013-10-05T20:33:47.680 に答える