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Date: Sat, 27 Apr 2013 09:51:44 -0700 (PDT)
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Subject: Re: Depth First Search of a Char_Matrix?
From: Alex <willmann817@gmail.com>
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Xref: news.eternal-september.org comp.lang.ada:15178
Date: 2013-04-27T09:51:44-07:00
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On Saturday, April 27, 2013 12:34:55 PM UTC-4, Shark8 wrote:
> On Saturday, April 27, 2013 10:27:23 AM UTC-6, Alex wrote:
>=20
> > On Saturday, April 27, 2013 10:09:10 AM UTC-4, Alex wrote:
>=20
> >=20
>=20
> > > Below is Char_Matrix representation of the board game "Go".  A 'W' re=
presents a white piece, a 'B' represents a black piece, and a '.' represent=
s a empty space.  Each black or white piece can either be alive or dead.  A=
 piece is Alive is if it horizontally or vertically next to a '.' OR if it =
is horizontally or vertically next to another piece that is alive. You can =
think of aliveness as being contagious.  How can I use depth first search t=
o count the number of alive black pieces and alive white pieces? =20
>=20
> >=20
>=20
> > >=20
>=20
> >=20
>=20
> > >=20
>=20
> >=20
>=20
> > >=20
>=20
> >=20
>=20
> > > WW.BB
>=20
> >=20
>=20
> > >=20
>=20
> >=20
>=20
> > > .WWWW
>=20
> >=20
>=20
> > >=20
>=20
> >=20
>=20
> > > WWBBB
>=20
> >=20
>=20
> > >=20
>=20
> >=20
>=20
> > > BBBWW
>=20
> >=20
>=20
> > >=20
>=20
> >=20
>=20
> > > WWBW.
>=20
> >=20
>=20
> > >=20
>=20
> >=20
>=20
> > >=20
>=20
> >=20
>=20
> > >=20
>=20
> >=20
>=20
> > >=20
>=20
> >=20
>=20
> > >=20
>=20
> >=20
>=20
> > > In this example there are 11 alive white piece and 2 alive black piec=
es.
>=20
> >=20
>=20
> > >=20
>=20
> >=20
>=20
> > >=20
>=20
> >=20
>=20
> > >=20
>=20
> >=20
>=20
> > > Can anyone provide any insight into this problem?
>=20
> >=20
>=20
> >=20
>=20
> >=20
>=20
> > Shark you are correct,  I forgot to include the fact that only like col=
ors are contagious.  Thank you very much for your assistance.  Without prov=
iding the code how would I change it to reflect this piece of missing logic=
?
>=20
>=20
>=20
> Simple:
>=20
> 1 )  Add a local variable indicating the color to Is_Alive, that will be =
accessable to its nested functions.
>=20
> 2 )  After checking for null on (x,y) assign that to the variable before =
calling recursion.
>=20
>=20
>=20
> You could also make that variable a constant and use a conditional expres=
sion [in Ada 2012] to set the initial value -- something like:
>=20
> Color : Constant Piece_Color:=3D (if board(x,y) /=3D null then board(x,y)=
.color else white); -- DEFAULT to white on NULL, otherwise set to the initi=
al piece's color.

Thanks! So I am given the function signature, not really a function body th=
at looks like this

   function Count_Alive(Board : Char_Matrix) return Integer is
 	M : Char_Matrix :=3D Board; =20
	begin
      return -999;
   end Count_Alive;


So I understand much of your logic, but I am given a matrix of characters d=
efined as such:

type Char_Matrix is array(Positive range <>, Positive range <>) of Characte=
r;

So could you give me like an algorithm in words on what I need to do instea=
d of giving me the answer in code?