# fannkuch-redux Dart #2 program

## source code

```/* 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
*/

fannkuch(n) {
var p = new List<int>(n), q = new List<int>(n), s = new List<int>(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 {
var 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++){
var 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(args) {
int n = args.length > 0 ? int.parse(args[0]) : 7;
var pf = fannkuch(n);
print("\${pf[0]}\nPfannkuchen(\$n) = \${pf[1]}");
}

```

## notes, command-line, and program output

```NOTES:
Dart SDK version: 2.10.0 (stable) (Mon Sep 28 09:21:23 2020 +0200) on "linux_x64"

Fri, 02 Oct 2020 00:01:34 GMT

MAKE:
/opt/src/dart-sdk/bin/dartanalyzer fannkuchredux.dart-2.dart
Analyzing fannkuchredux.dart-2.dart...
No issues found!

3.43s to complete and log all make actions

COMMAND LINE:
/opt/src/dart-sdk/bin/dart  fannkuchredux.dart-2.dart 12

PROGRAM OUTPUT:
3968050
Pfannkuchen(12) = 65
```