```>
> Cookie Monster is trying to walk through the Cookie Forest and consume
> as many cookies as possible. However, there are many different paths
> that Cookie Monster can take, and he isn't sure which way is the best
> way. Help him eat as many cookies as possible by writing a program
> which finds the optimal path from the upper left part of the forest to
> the bottom right. Cookie Monster can only move south and east. There
> are also several thorn patches through which he cannot cross. The
> forest can be represented as a grid of numbers, where the number
> represents the amount of cookies in that acre and -1 represents an
> impassible thorn patch. An example forest is provided below:
>

Here is my solution.
It only works for square forests.
It finds and stores every possible path then outputs the best one.
So, it is not very fast ( about 30 sec. ).
But it is short and (hopefully) easy to read.

str = <<DATA
1  3  0  5 -1  7 -1 -1  0  4  2  1
-1  3  2  1 -1  4 -1  5  3 -1  1  0
5  4  8 -1  3  2  2 -1  4 -1  0  0
2  1  0  4  1 -1  8  0  2 -1  2  5
1  4  0  1 -1  0  3  2  2  4  1  4
0  1  4  1  1  6  1  4  5  2  1  0
3  2  5  2  0  7 -1  2  1  0 -1  3
0 -1  4 -1 -1  3  5  1  4  2  1  2
5  4  8 -1  3  2  2 -1  4 -1  0  0
2  1  0  4  1 -1  8  0  2 -1  2  5
1  3  0  5 -1  7 -1 -1  0  4  2  1
0  0  3  1  5  2  1  5  4  1  3  3
DATA

forest, choices, paths = [],[],[]
str.each {|x| forest << x.strip.split(/\s+/).map{|x| x.to_i}}
top = forest[0].length - 1
nums = (0..top).map {Array.new}
(0...2**top).each do |x|
nums[x.to_s(2).split(//).map{|f| f.to_i}.inject{|a,b| a+b}] <<
x.to_s(2).rjust(top,"0")
end

(0..top).each{|x| nums[x].each{|y| nums[top-x].each{|z| choices << (y+z)}}}

choices.each do |a|
trypath = []
south,east = 0,0
trypath << forest[south][east]
a.split(//).each do |c|
south += 1 if c == "0"
east += 1 if c == "1"
trypath << forest[south][east]
break if forest[south][east] == -1
end
paths << trypath unless trypath.include?(-1)
end

p paths.max{|x,y| x.inject{|a,b| a+b} <=> y.inject{|a,b| a+b} }

Harry

--
A Look into Japanese Ruby List in English
http://www.kakueki.com/ruby/list.html

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