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  1. let combine (a, a') (b, b') = 
  2.     seq { 
  3.         yield a + b, sprintf "(%s + %s)" a' b'
  4.         if Seq.last a' <> ')' && Seq.head b' <> '(' 
  5.                 then yield a * 10 + b, sprintf "%s%s" a' b' else ()
  6.         yield a - b, sprintf "(%s - %s)" a' b'
  7.         yield a * b, sprintf "(%s * %s)" a' b'
  8.         if b <> 0 && a / b * b = a
  9.                 then yield a / b, sprintf "(a / b)" else ()
  10.         } 
  11.  
  12. let rec solve xs = 
  13.     seq {
  14.         match xs with
  15.         | a :: b :: [] -> yield! combine a b
  16.         | a :: b :: t  -> yield! combine a b |> Seq.collect (fun e -> solve (e :: t))
  17.                           yield! solve (b :: t) |> Seq.collect (fun t -> solve (a :: t :: []))
  18.         | x :: []      -> yield x
  19.         | []           -> ()
  20.         }
  21.  
  22. let f xs n = 
  23.     xs |> List.map (fun e -> e, string e) 
  24.        |> solve
  25.        |> Seq.filter (fst >> ((=)n))
  26.  
  27. do
  28.     for x, e in f [8; 9; 4; 3; 9; 2] 100 do 
  29.         printfn "%A = %s" x e
Success #stdin #stdout 0.29s 26616KB
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100 = (((89 - 4) - 3) + (9 * 2))
100 = ((89 - 4) - (3 - (9 * 2)))
100 = (89 - ((4 + 3) - (9 * 2)))
100 = (89 + (((4 - 3) * 9) + 2))
100 = (89 + ((4 - 3) * (9 + 2)))
100 = (89 - (4 + (3 - (9 * 2))))
100 = (((8 * 9) + 4) + ((3 + 9) * 2))
100 = ((8 * 9) + (4 + ((3 + 9) * 2)))
100 = (8 + ((((9 + 4) - 3) * 9) + 2))
https://ideone.com/DsdPmQ
language:
F# (mono 4.1)
created:
9 years ago
visibility:
public

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