Solution to Ancient City Ruby 2016

snake_case.rb

# I gave a take about Enumerator at ACR so naturally 
# I had to solve the Snake Case challenge using one.
module SnakeCase
  module_function

  # Returns the number of paths for a 
  # grid given by m x n blocks
  # 
  # @param m [Fixnum] width
  # @param n [Fixnum] length
  # @return [Fixnum] number of paths
  def paths(m, n)
    pascal.take(m+n)[-1][n]
  end
  
  # Returns a sequence of arrays representing
  # pascals triangle where the values in each
  # "row" represent the sum of adjacent row values
  # in the preceding row
  # 
  # @return [Array] an array of arrays
  def pascal(rows = [1])
    Enumerator.new do |y|
      loop { y.yield(rows = ([0] + rows).zip(rows + [0]).map { |a, b| a + b }) }
    end
  end
end

SnakeCase.paths(10, 10)