69 lines
1.8 KiB
Nim
69 lines
1.8 KiB
Nim
import os
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import strutils
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proc fannkuch(n: int): int =
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var
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count: seq[int]
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maxFlips = 0
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m = n-1
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r = n
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check = 0
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perm1: seq[int]
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perm: seq[int]
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newSeq(count, n+1)
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newSeq(perm1, n)
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newSeq(perm, n)
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for i in 0 .. n-1:
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count[i] = i+1
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perm1[i] = i
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perm[i] = i
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count[n] = n+1
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while true:
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if check < 30:
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for i in items(perm1):
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write(stdout, $(i+1))
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echo("")
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inc(check)
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while r != 1:
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count[r-1] = r
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dec (r)
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if perm1[0] != 0 and perm1[m] != m:
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# perm = perm1
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# The above line is between 3 and 4 times slower than the loop below!
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for i in 0 .. n-1:
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perm[i] = perm1[i]
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var flipsCount = 0
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var k = perm[0]
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while k != 0:
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for i in 0 .. (k div 2):
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swap(perm[i], perm[k-i])
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inc(flipsCount)
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k = perm[0]
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if flipsCount > maxFlips:
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maxFlips = flipsCount
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block makePerm:
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while r != n:
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var tmp = perm1[0]
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# # perm1.delete (0)
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# # perm1.insert (tmp, r)
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# # The above is about twice as slow as the following:
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# moveMem (addr (perm1[0]), addr (perm1[1]), r * sizeof (int))
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# The call to moveMem is about 50% slower than the loop below!
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for i in 0 .. r-1:
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perm1[i] = perm1[i+1]
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perm1[r] = tmp
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dec(count[r])
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if count[r] > 0:
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break makePerm
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inc(r)
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return maxFlips
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var n = 10
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echo("Pfannkuchen(" & $n & ") = " & $fannkuch(n))
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