The Computer Language
Benchmarks Game

fannkuch-redux Java #2 program

source code

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

   contributed by Isaac Gouy
   converted to Java by Oleg Mazurov
*/

public class fannkuchredux
{
   public static int fannkuch(int n) {
      int[] perm = new int[n];
      int[] perm1 = new int[n];
      int[] count = new int[n];
      int maxFlipsCount = 0;
      int permCount = 0;
      int checksum = 0;

      for(int i=0; i<n; i++) perm1[i] = i;
      int r = n;

      while (true) {

         while (r != 1){ count[r-1] = r; r--; }

         for(int i=0; i<n; i++) perm[i] = perm1[i];
         int flipsCount = 0;
         int k;

         while ( !((k=perm[0]) == 0) ) {
            int k2 = (k+1) >> 1;
            for(int i=0; i<k2; i++) {
               int temp = perm[i]; perm[i] = perm[k-i]; perm[k-i] = temp;
            }
            flipsCount++;
         }

         maxFlipsCount = Math.max(maxFlipsCount, flipsCount);
         checksum += permCount%2 == 0 ? flipsCount : -flipsCount;

         // Use incremental change to generate another permutation
         while (true) {
            if (r == n) {
	       System.out.println( checksum );
	       return maxFlipsCount;
	    }
            int perm0 = perm1[0];
            int i = 0;
            while (i < r) {
               int j = i + 1;
               perm1[i] = perm1[j];
               i = j;
            }
            perm1[r] = perm0;

            count[r] = count[r] - 1;
            if (count[r] > 0) break;
            r++;
         }

         permCount++;
      }
   }

   public static void main(String[] args){
      int n = 7;
      if (args.length > 0) n = Integer.parseInt(args[0]);
      System.out.println("Pfannkuchen("+n+") = "+fannkuch(n));
   }
}
    

notes, command-line, and program output

NOTES:
64-bit Ubuntu quad core
java version "1.8.0_121"
Java(TM) SE Runtime Environment (build 1.8.0_121-b13)
Java HotSpot(TM) 64-Bit Server VM (build 25.121-b13, mixed mode)


Sat, 15 Apr 2017 16:39:51 GMT

MAKE:
mv fannkuchredux.java-2.java fannkuchredux.java
/usr/local/src/jdk1.8.0_121/bin/javac -d .  fannkuchredux.java
0.74s to complete and log all make actions

COMMAND LINE:
/usr/local/src/jdk1.8.0_121/bin/java   fannkuchredux 12

PROGRAM OUTPUT:
3968050
Pfannkuchen(12) = 65