39 lines
833 B
Nim
39 lines
833 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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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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var rc : proc(np: int)
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rc = proc(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) # recurs 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) # recurs swap
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let w = s[0]
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s[0..<pp] = s[1..pp]
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s[pp] = w
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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(seq: openArray[int])=
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echo seq
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)
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