daily_challenge_1.rb

def remove_first_and_last_letters(str)
  return '' if str.length <= 2
  str[1..-2]
end

puts remove_first_and_last_letters('foo')
puts remove_first_and_last_letters('hi')
puts remove_first_and_last_letters('x')
puts remove_first_and_last_letters('xHello, world!D')

daily_challenge_2.rb

def diamond(num)
  return if num < 0
  return if num.even?

  [
    (1..num).step(2), (1...num).step(2).reverse_each
  ].each do |range|
    range.each do |i|
      dias = '*' * i
      puts dias.center(num)
    end
  end
end

diamond(1)
diamond(3)
diamond(11)
diamond(2)
diamond(-11)