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Problem 4 - ECOO

#!/usr/bin/env ruby

# Problem 4
# ECOO 2011 Perimeter Trees
# Andrew Horsman

class Point < Struct.new(:x, :y); end
class Line

  def initialize(x1, y1, x2, y2)
    @x1, @y1, @x2, @y2 = x1.to_f, y1, x2, y2
    calculate_slope
  end 

  def calculate_slope
    @m = (@y2 - @y1) / (@x2 - @x1)
  end

  def calculate_y(x)
    @m * x - @x1 * @m + @y1 
  end

  def check_above(x, y)
    y > calculate_y(x)
  end

  def check_below(x, y)
    y < calculate_y(x)
  end

end

class Run

  def initialize(data)
    lines  = data.split("\n")
    groves = []

    until lines.length == 0
      num_lines = lines.slice!(0).to_i
      data_set  = []

      num_lines.times { data_set << lines.slice!(0).strip }
      groves << data_set
    end

    groves.each { |grove| run grove }
  end

  def run(data_set)
    trees = data_set.map { |xy| Point.new(*xy.split(" ").map { |arg| arg.to_i }) }
    number_of_perimeter_trees = 0

    trees.each_with_index do |tree_for_checking, index_one|
      
      is_perimeter_tree = false  

      other_trees = trees.dup
      other_trees.slice! index_one
      other_trees.each_with_index do |tree_for_line, index_two|

        number_of_above_trees = 0
        number_of_below_trees = 0
        line = Line.new(tree_for_checking.x, tree_for_checking.y, tree_for_line.x, tree_for_line.y)

        non_line_trees = other_trees.dup
        non_line_trees.slice! index_two
        non_line_trees.each do |check_tree|
          if line.check_above(check_tree.x, check_tree.y) 
            number_of_above_trees += 1
          elsif line.check_below(check_tree.x, check_tree.y)
            number_of_below_trees += 1
          end
          break if number_of_above_trees > 0 and number_of_below_trees > 0
        end

        is_perimeter_tree = !(number_of_above_trees > 0 and number_of_below_trees > 0)
        break if is_perimeter_tree

      end

      number_of_perimeter_trees += 1 if is_perimeter_tree

    end

    puts "There are #{number_of_perimeter_trees} perimeter trees in a grove of #{trees.length} trees."  

  end

end

%w(
  data41.txt
  test.txt
).each do |file_name|
  puts "Running #{file_name}"
  run = Run.new(File.read(file_name))
end

Proving to @ProgrammerMike that my method would've worked.