The Computer Language
Benchmarks Game

fannkuch-redux Swift program

source code

/* The Computer Language Benchmarks Game
   http://benchmarksgame.alioth.debian.org/

   contributed by Isaac Gouy
   transliterated from Rex Kerr's Scala program 
*/


func fannkuch(_ n: Int) -> Int {
   var perm = Array(repeating: 0, count: n),
      count = Array(repeating: 0, count: n)

   var perm1 = Array(repeating: 0, count: n)
   for j in 0...n-1 { perm1[j] = j }

   var f = 0, i = 0, k = 0, r = 0, flips = 0, nperm = 0, checksum = 0

   r = n
   while r > 0 {
      i = 0
      while r != 1 { count[r-1] = r; r -= 1 }
      while i < n { perm[i] = perm1[i]; i += 1 }

      // Count flips and update max  and checksum
      f = 0
      k = perm[0]
      while k != 0 {
         i = 0
         while 2*i < k {
            let t = perm[i]; perm[i] = perm[k-i]; perm[k-i] = t
            i += 1
         }
         k = perm[0]
         f += 1
      }
      if f>flips { flips = f }
      if (nperm&0x1)==0 { checksum += f } else { checksum -= f }

      // Use incremental change to generate another permutation
      var go = true
      while go {
         if r == n {
            print(checksum)
            return flips
         }
         let p0 = perm1[0]
         i = 0
         while i < r {
            let j = i+1
            perm1[i] = perm1[j]
            i = j
         }
         perm1[r] = p0

         count[r] -= 1
         if count[r] > 0 { go = false } else { r += 1 }
      }
      nperm += 1
   }
   return flips
}


let n: Int = Int(CommandLine.arguments[1])!
print("Pfannkuchen(\(n)) = \(fannkuch(n))")


    

notes, command-line, and program output

NOTES:
64-bit Ubuntu quad core
Swift version 4.1-dev (LLVM 3fa7aed3df, Clang 529966cf07, Swift 607f23d66d)
Target: x86_64-unknown-linux-gnu




Wed, 15 Nov 2017 19:01:00 GMT

MAKE:
/opt/src/swift-4.1-DEVELOPMENT-SNAPSHOT-2017-11-06-a-ubuntu16.10/usr/bin/swiftc fannkuchredux.swift -Ounchecked  -o fannkuchredux.swift_run

2.36s to complete and log all make actions

COMMAND LINE:
./fannkuchredux.swift_run 12

PROGRAM OUTPUT:
3968050
Pfannkuchen(12) = 65