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Subject: Re: depth first search
Date: Sun, 28 Apr 2013 21:43:33 -0500
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On 4/27/2013 11:46 PM, willmann817@gmail.com wrote:
> I am given method signature that takes a square 2D Character Array (a
> matrix) that represents a board of a game called Go.  The board has
> black pieces represented by a 'B' white pieces represented by a 'W'
> and empty spaces represented by '.' The board also has a padding to
> represent going off the board this padding on all sides is
> represented by the character '/'.  A piece is considered alive if it
> is horizontally or vertically next to an empty space and alive pieces
> are contagious to other alive pieces of the same color. Using depth
> first search how can I count the number of alive black pieces and
> alive white pieces?  I only know how to use DFS on a graph data type
> not a 2D array.

The algorithm you are looking for is more properly called the "flood 
fill" algorithm; the name is derived from the notion that filling the region

Note that a 2-D grid is itself a graph; the adjacency lists are just 
implicit in the definition. Consider:

o-o-o-o
| | | |
o-o-o-o
| | | |
o-o-o-o
| | | |
o-o-o-o

[Note that you need fixed-width fonts for the above diagram to make any 
sense.]

If that still isn't enough for you, consider that you want to find the 
connected components of a graph where edges between differently-colored 
nodes are deleted, e.g.:

B-B W-W
|   | |
B W-W-W
|
B * B-B
| |
B *-*-*

-- 
Beware of bugs in the above code; I have only proved it correct, not
tried it. -- Donald E. Knuth