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digitalmars.D.learn - I do not understand what the problem is in this code.

reply 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);
}
Mar 02
parent reply 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
Mar 02
parent 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!!!
Mar 03