euler/ruby/euler018.rb

triangle = [[75],
            [95,64],
            [17,47,82],
            [18,35,87,10],
            [20, 4,82,47,65],
            [19, 1,23,75, 3,34],
            [88, 2,77,73, 7,63,67],
            [99,65, 4,28, 6,16,70,92],
            [41,41,26,56,83,40,80,70,33],
            [41,48,72,33,47,32,37,16,94,29],
            [53,71,44,65,25,43,91,52,97,51,14],
            [70,11,33,28,77,73,17,78,39,68,17,57],
            [91,71,52,38,17,14,91,43,58,50,27,29,28],
            [63,66, 4,68,89,53,67,30,73,16,69,87,40,31],
            [ 4,62,98,27,23, 9,70,98,73,93,38,53,60, 4,23]]

class Triangle
  def initialize(list_of_lists)
    @data = list_of_lists
    @route_length = {}
    locations.each do |location|
      @route_length[location] = @data[location.first][location.last]
    end
  end

  def locations
    locations = []
    (0..row_count-1).each do |row_num|
      (0..row_num).each do |index|
        locations << [row_num, index]
      end
    end
    locations
  end

  def row(num)
    @data[num]
  end

  def row_count
    @data.count
  end

  def route_length(row, index_from_left)
    @route_length[[row, index_from_left]]
  end

  def root
    @data.first.first
  end

  def element(row_num, index_from_left)
    row(row_num)[index_from_left]
  end

  def children_of_element(row_num, index_from_left)
    unless is_bottom_row?(row_num)
      [@route_length[[row_num+1, index_from_left]], @route_length[[row_num+1, index_from_left+1]]]
    else
      []
    end
  end

  def is_bottom_row?(row_num)
    row_num == @data.count - 1
  end

  def bottom_row
    @data.count - 1
  end

  def maximum_route_total
    ((bottom_row-1).downto(0)).each do |row_num|
      (0..@data[row_num].length-1).each do |index|
        children = children_of_element(row_num, index)
        current_elt = element(row_num, index)
        choose_first_elt = current_elt + children.first
        choose_second_elt = current_elt + children.last
        @route_length[[row_num, index]] = [choose_first_elt, choose_second_elt].max
      end
    end
    @route_length[[0,0]]
  end
end

def parse_triangle(filename)
  triangle_data = []
  File.open(filename, 'r') do |file|
    while line = file.gets
      triangle_data << line.split(" ").map(&:to_i)
    end
  end
  Triangle.new(triangle_data)
end

parsed_triangle = parse_triangle("triangle18.txt")

triangle_two = Triangle.new([ [3],
                          [7,4],
                          [2,4,6],
                          [8,5,9,3] ])

triangle_67 = parse_triangle("triangle67.txt")

puts triangle_two.maximum_route_total.inspect
puts parsed_triangle.maximum_route_total.inspect
puts triangle_67.maximum_route_total.inspect