• steven kladitis (13/13) Mar 02 2017 void main() {
• Jordan Wilson (28/41) Mar 02 2017 I saw this answer for a similar question from Adam D. Ruppe:
• steven kladitis (2/14) Mar 03 2017 added std.conv and it works!! thanks for the help!!!

steven kladitis <steven_kladitis yahoo.com> writes:

void main() {
     import std.stdio, std.range, std.algorithm, std.string;

     const pieces = "KQRrBbNN";
     alias I = indexOf;
     auto starts = permutations(pieces.dup).filter!(p =>
             I(p, 'B') % 2 != I(p, 'b') % 2 && // Bishop 
constraint.
             // King constraint.
             ((I(p, 'r') < I(p, 'K') && I(p, 'K') < I(p, 'R')) ||
              (I(p, 'R') < I(p, 'K') && I(p, 'K') < I(p, 'r'))))
         .map!toUpper.array.sort().uniq;
     writeln(starts.walkLength, "\n", starts.front);
}

Jordan Wilson <wilsonjord gmail.com> writes:

On Friday, 3 March 2017 at 03:11:24 UTC, steven kladitis wrote:
 void main() {
     import std.stdio, std.range, std.algorithm, std.string;

     const pieces = "KQRrBbNN";
     alias I = indexOf;
     auto starts = permutations(pieces.dup).filter!(p =>
             I(p, 'B') % 2 != I(p, 'b') % 2 && // Bishop 
 constraint.
             // King constraint.
             ((I(p, 'r') < I(p, 'K') && I(p, 'K') < I(p, 'R')) ||
              (I(p, 'R') < I(p, 'K') && I(p, 'K') < I(p, 'r'))))
         .map!toUpper.array.sort().uniq;
     writeln(starts.walkLength, "\n", starts.front);
 }

I saw this answer for a similar question from Adam D. Ruppe:
Quote:
"...it is anything that Phobos considers "bidirectional" and 
"swappable" - an array it can reverse easily and swap individual 
elements, and it considers plain string to be non-swappable due 
to UTF-8 encoding. Due to its variable length element encoding, 
swapping two chars may require reshuffling the entire array, 
which would be far more expensive than the function allows.

Thus, the easiest way to make this work is to use a type which 
Phobos considers to be swappable: a UTF-32 string, aka dchar[]."

So, here's my attempt at something that might work for you:
     const pieces = "KQRrBbNN";
     alias I = indexOf;
     auto starts = permutations(pieces.to!(dchar[])).filter!(p =>
             I(p, 'B') % 2 != I(p, 'b') % 2 && // Bishop 
constraint.
             // King constraint.
             ((I(p, 'r') < I(p, 'K') && I(p, 'K') < I(p, 'R')) ||
              (I(p, 'R') < I(p, 'K') && I(p, 'K') < I(p, 'r'))))
         .map!(to!string)
         .map!(toUpper).array.sort().uniq;
         writeln(starts.walkLength, "\n", starts.front);

Note: the ".map!(to!string)" part was just to get round dealing 
with the fact that permutations returns an Index.

It's may not be exactly what you want, but hopefully set you on 
the right track.

Jordan

steven kladitis <steven_kladitis yahoo.com> writes:

On Friday, 3 March 2017 at 04:14:02 UTC, Jordan Wilson wrote:
 On Friday, 3 March 2017 at 03:11:24 UTC, steven kladitis wrote:
 [...]

 I saw this answer for a similar question from Adam D. Ruppe:
 Quote:
 "...it is anything that Phobos considers "bidirectional" and 
 "swappable" - an array it can reverse easily and swap 
 individual elements, and it considers plain string to be 
 non-swappable due to UTF-8 encoding. Due to its variable length 
 element encoding, swapping two chars may require reshuffling 
 the entire array, which would be far more expensive than the 
 function allows.

 [...]

added std.conv and it works!! thanks for the help!!!