gistfile1.rb

# Copyright © 2004-2013 Brent Fulgham
#
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#
# Redistribution and use in source and binary forms, with or without
# modification, are permitted provided that the following conditions are met:
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#     this list of conditions and the following disclaimer.
#
#   * Redistributions in binary form must reproduce the above copyright notice,
#     this list of conditions and the following disclaimer in the documentation
#     and/or other materials provided with the distribution.
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#   * Neither the name of "The Computer Language Benchmarks Game" nor the name
#     of "The Computer Language Shootout Benchmarks" nor the names of its
#     contributors may be used to endorse or promote products derived from this
#     software without specific prior written permission.
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# The Computer Language Benchmarks Game

# http://benchmarksgame.alioth.debian.org/

# Contributed by Wesley Moxam

# Modified by Sokolov Yura aka funny_falcon

# http://benchmarksgame.alioth.debian.org/u64q/program.php?test=fannkuchredux&lang=yarv&id=1

def fannkuch(n)
  p = (0..n).to_a
  s = p.dup
  q = p.dup
  sign = 1
  sum = maxflips = 0
  while(true)
    # flip.

    if (q1 = p[1]) != 1
      q[0..-1] = p
      flips = 1
      until (qq = q[q1]) == 1
        q[q1] = q1
        if q1 >= 4
          i, j = 2, q1 - 1
          while i < j
            q[i], q[j] = q[j], q[i]
            i += 1
            j -= 1
          end
        end
        q1 = qq
        flips += 1
      end
      sum += sign * flips
      maxflips = flips if flips > maxflips # New maximum?

    end
    # Permute.

    if sign == 1
      # Rotate 1<-2.

      p[1], p[2] = p[2], p[1]
      sign = -1
    else
      # Rotate 1<-2 and 1<-2<-3.

      p[2], p[3] = p[3], p[2]
      sign = 1
      i = 3
      while i <= n && s[i] == 1
        #return [sum, maxflips] if i == n     # Out of permutations.
        return sum if i == n

        s[i] = i
        # Rotate 1<-...<-i+1.

        t = p.delete_at(1)
        i += 1
        p.insert(i, t)
      end
      s[i] -= 1  if i <= n
    end
  end
end

loop do
  start = Time.now
  fannkuch(9)
  puts Time.now - start
end