problem_28.rb

# Starting with the number 1 and moving to the right in a clockwise direction a 5 by 5 spiral is formed as follows:

# 21 22 23 24 25
# 20  7  8  9 10
# 19  6  1  2 11
# 18  5  4  3 12
# 17 16 15 14 13

# It can be verified that the sum of the numbers on the diagonals is 101.

# What is the sum of the numbers on the diagonals in a 1001 by 1001 spiral formed in the same way?

diagonal_numbers = [1]

(1..1000).to_a.each do |number|
  if number % 2 == 0
    diagonal_numbers << diagonal_numbers[-1] + number
    diagonal_numbers << diagonal_numbers[-1] + number
    diagonal_numbers << diagonal_numbers[-1] + number
    diagonal_numbers << diagonal_numbers[-1] + number
  else
    next
  end
end

p diagonal_numbers
p diagonal_numbers.inject(:+)