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60 lines
1.8 KiB
Plaintext
60 lines
1.8 KiB
Plaintext
app "quicksort"
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packages { pf: "quicksort-platform/main.roc" }
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imports []
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provides [quicksort] to pf
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quicksort = \originalList ->
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n = List.len originalList
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quicksortHelp originalList 0 (n - 1)
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quicksortHelp : List (Num a), Nat, Nat -> List (Num a)
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quicksortHelp = \list, low, high ->
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if low < high then
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when partition low high list is
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Pair partitionIndex partitioned ->
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partitioned
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|> quicksortHelp low (partitionIndex - 1)
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|> quicksortHelp (partitionIndex + 1) high
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else
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list
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partition : Nat, Nat, List (Num a) -> [Pair Nat (List (Num a))]
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partition = \low, high, initialList ->
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when List.get initialList high is
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Ok pivot ->
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when partitionHelp low low initialList high pivot is
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Pair newI newList ->
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Pair newI (swap newI high newList)
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Err _ ->
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Pair low initialList
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partitionHelp : Nat, Nat, List (Num c), Nat, Num c -> [Pair Nat (List (Num c))]
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partitionHelp = \i, j, list, high, pivot ->
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if j < high then
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when List.get list j is
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Ok value ->
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if value <= pivot then
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partitionHelp (i + 1) (j + 1) (swap i j list) high pivot
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else
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partitionHelp i (j + 1) list high pivot
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Err _ ->
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Pair i list
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else
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Pair i list
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swap : Nat, Nat, List a -> List a
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swap = \i, j, list ->
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when Pair (List.get list i) (List.get list j) is
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Pair (Ok atI) (Ok atJ) ->
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list
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|> List.set i atJ
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|> List.set j atI
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_ ->
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# to prevent a decrement on list
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# turns out this is very important for optimizations
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list
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