28 lines
502 B
Nim
28 lines
502 B
Nim
# iterative Boothroyd method
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iterator permutations[T](ys: openarray[T]): seq[T] =
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var
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d = 1
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c = newSeq[int](ys.len)
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xs = newSeq[T](ys.len)
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for i, y in ys: xs[i] = y
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yield xs
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block outer:
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while true:
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while d > 1:
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dec d
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c[d] = 0
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while c[d] >= d:
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inc d
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if d >= ys.len: break outer
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let i = if (d and 1) == 1: c[d] else: 0
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swap xs[i], xs[d]
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yield xs
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inc c[d]
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var x = @[1,2,3]
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for i in permutations(x):
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echo i
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