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56 lines
1.3 KiB
Plaintext
56 lines
1.3 KiB
Plaintext
app "nqueens"
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packages { base: "platform" }
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imports [base.Task]
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provides [ main ] to base
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main : Task.Task {} []
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main =
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# Task.after Task.getInt \n ->
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queens 6
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|> Str.fromInt
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|> Task.putLine
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ConsList a : [ Nil, Cons a (ConsList a) ]
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queens = \n -> length (findSolutions n n)
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length : ConsList a -> I64
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length = \xs -> lengthHelp xs 0
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lengthHelp : ConsList a, I64 -> I64
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lengthHelp = \foobar, acc ->
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when foobar is
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Cons _ lrest -> lengthHelp lrest (1 + acc)
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Nil -> acc
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safe : I64, I64, ConsList I64 -> Bool
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safe = \queen, diagonal, xs ->
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when xs is
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Nil ->
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True
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Cons q t ->
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queen != q && queen != q + diagonal && queen != q - diagonal && safe queen (diagonal + 1) t
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appendSafe : I64, ConsList I64, ConsList (ConsList I64) -> ConsList (ConsList I64)
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appendSafe = \k, soln, solns ->
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if k <= 0 then
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solns
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else if safe k 1 soln then
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appendSafe (k - 1) soln (Cons (Cons k soln) solns)
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else
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appendSafe (k - 1) soln solns
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extend = \n, acc, solutions ->
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when solutions is
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Nil -> acc
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Cons soln rest -> extend n (appendSafe n soln acc) rest
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findSolutions = \n, k ->
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if k == 0 then
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Cons Nil Nil
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else
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extend n Nil (findSolutions n (k - 1))
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