Bending a two-dimensional array to the left and right to get every diagonal path.

diagonals.rb

def diagonal_coords(size)
  left_array = push_array(size, :left)
  right_array = push_array(size, :right)
  [left_array, right_array].flatten(1)
end

def push_array(size, direction)
  array = Array.new(size) { |x| Array.new(size) { |y| [x,y] }}
  size.times do |i|
    case direction
    when :right then right = size - 1 - left = i
    when :left then left = size - 1 - right = i
    end
    right.times do
      array[i].unshift(nil)
    end
    left.times do
      array[i] << nil
    end
  end
  array.transpose.map(&:compact)
end

diagonal_coords(6)
 # => [[[0, 0]],
 #     [[0, 1], [1, 0]],
 #     [[0, 2], [1, 1], [2, 0]],
 #     [[0, 3], [1, 2], [2, 1], [3, 0]],
 #     [[0, 4], [1, 3], [2, 2], [3, 1], [4, 0]],
 #     [[0, 5], [1, 4], [2, 3], [3, 2], [4, 1], [5, 0]],
 #     [[1, 5], [2, 4], [3, 3], [4, 2], [5, 1]],
 #     [[2, 5], [3, 4], [4, 3], [5, 2]],
 #     [[3, 5], [4, 4], [5, 3]],
 #     [[4, 5], [5, 4]],
 #     [[5, 5]],
 #     [[5, 0]],
 #     [[4, 0], [5, 1]],
 #     [[3, 0], [4, 1], [5, 2]],
 #     [[2, 0], [3, 1], [4, 2], [5, 3]],
 #     [[1, 0], [2, 1], [3, 2], [4, 3], [5, 4]],
 #     [[0, 0], [1, 1], [2, 2], [3, 3], [4, 4], [5, 5]],
 #     [[0, 1], [1, 2], [2, 3], [3, 4], [4, 5]],
 #     [[0, 2], [1, 3], [2, 4], [3, 5]],
 #     [[0, 3], [1, 4], [2, 5]],
 #     [[0, 4], [1, 5]],
 #     [[0, 5]]]