34 lines
702 B
Nim
34 lines
702 B
Nim
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# Nim implementation of the (very fast) Go example.
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# http://rosettacode.org/wiki/Permutations#Go
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# implementing a recursive https://en.wikipedia.org/wiki/Steinhaus–Johnson–Trotter_algorithm
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import algorithm
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proc perm(s: openArray[int]; emit: proc(emit: openArray[int])) =
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var s = @s
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if s.len == 0:
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emit(s)
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return
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proc rc(np: int) =
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if np == 1:
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emit(s)
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return
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var
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np1 = np - 1
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pp = s.len - np1
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rc(np1) # Recurse prior swaps.
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for i in countDown(pp, 1):
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swap s[i], s[i-1]
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rc(np1) # Recurse swap.
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s.rotateLeft(0..pp, 1)
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rc(s.len)
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var se = @[0, 1, 2, 3] #, 4, 5, 6, 7, 8, 9, 10]
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perm(se, proc(s: openArray[int])= echo s)
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