fannkuch-redux Dart #3 program

/* The Computer Language Benchmarks Game
   https://salsa.debian.org/benchmarksgame-team/benchmarksgame/

   contributed by Jos Hirth
   (previously used) warmup code suggested by Vyacheslav Egorov
   transliterated from Isaac Gouy's C# program,
   which was transliterated from Mike Pall's Lua program
   + null safety & Int32List by Isaac Gouy
*/

import 'dart:typed_data';

List<int> fannkuch(int n) {
  var p = Int32List(n), q = Int32List(n), s = Int32List(n);
  int sign = 1, maxflips = 0, sum = 0, m = n - 1;
  for (int i = 0; i < n; i++) {
    p[i] = i;
    q[i] = i;
    s[i] = i;
  }
  do {
    // Copy and flip.
    var q0 = p[0]; // Cache 0th element.
    if (q0 != 0) {
      for (int i = 1; i < n; i++) q[i] = p[i]; // Work on a copy.
      var flips = 1;
      do {
        final qq = q[q0];
        if (qq == 0) {
          // ... until 0th element is 0.
          sum += sign * flips;
          if (flips > maxflips) maxflips = flips; // New maximum?
          break;
        }
        q[q0] = q0;
        if (q0 >= 3) {
          int i = 1, j = q0 - 1, t;
          do {
            t = q[i];
            q[i] = q[j];
            q[j] = t;
            i++;
            j--;
          } while (i < j);
        }
        q0 = qq;
        flips++;
      } while (true);
    }
    // Permute.
    if (sign == 1) {
      var t = p[1];
      p[1] = p[0];
      p[0] = t;
      sign = -1; // Rotate 0<-1.
    } else {
      var t = p[1];
      p[1] = p[2];
      p[2] = t;
      sign = 1; // Rotate 0<-1 and 0<-1<-2.
      for (int i = 2; i < n; i++) {
        final sx = s[i];
        if (sx != 0) {
          s[i] = sx - 1;
          break;
        }
        if (i == m) return [sum, maxflips]; // Out of permutations.
        s[i] = i;
        // Rotate 0<-...<-i+1.
        t = p[0];
        for (int j = 0; j <= i; j++) {
          p[j] = p[j + 1];
        }
        p[i + 1] = t;
      }
    }
  } while (true);
}

void main(List<String> args) {
  final n = (args.length > 0) ? int.parse(args[0]) : 7;
  var pf = fannkuch(n);
  print("${pf[0]}\nPfannkuchen($n) = ${pf[1]}");
}
    

NOTES:
64-bit Ubuntu quad core
Dart SDK version: 3.5.4 (stable)
Wed Oct 16 16:18:51 2024



 Wed, 23 Oct 2024 02:49:55 GMT

MAKE:
/opt/src/dart-sdk/bin/dart analyze 
Analyzing tmp...
No issues found!

/opt/src/dart-sdk/bin/dart compile exe fannkuchredux.dartexe-3.dartexe -o fannkuchredux.dartexe-3.dartexe_run
Generated: /home/dunham/all-benchmarksgame/benchmarksgame_i53330/fannkuchredux/tmp/fannkuchredux.dartexe-3.dartexe_run

6.40s to complete and log all make actions

COMMAND LINE:
 ./fannkuchredux.dartexe-3.dartexe_run 12

PROGRAM OUTPUT:
3968050
Pfannkuchen(12) = 65