codegolf_solutions.rb

def luhn?(ccn)
  ccn = ccn.split(//).map! {|x| x.to_i}
  1.upto(ccn.size/2) do |i| 
    n = ccn[-i*2] * 2 
    ccn[-i*2] = n < 10 ? n : (n/10) + (n%10)
  end 
  ccn.inject(0) {|sum, x| sum += x} % 10 == 0
end

puts "Luhn Data"
puts luhn?("4111111111111111")
puts luhn?("4111111111111112")
puts luhn?("5105105105105100")
puts luhn?("4222222222222")

def ccexp?(s)
  parts = s.split('/').map! {|x| x.to_i}
  parts[1] -= 2000 if parts[1] > 100 # shouldn't need this.
  (parts.last*12 + parts.first - 1) <= (12*10 + 5)
end

puts "Credit Card Expire"
puts ccexp?("01/2000")
puts ccexp?("1/2000")
puts ccexp?("06/2010")
puts ccexp?("07/2010")
puts ccexp?("05/2015")


def mask(s)
  s[6..-5] = '*' * (s.size-10)
  s
end

puts "Masking"
puts mask("4111111111111111")
puts mask("512351235123")

def fibsum(n)
  return n if n <= 2
  two = [1, 1]
  sum = 2
  3.upto(n) do
    two[0], two[1] = two[1], two[0] + two[1]
    sum += two[1]
  end
  sum
end

puts "Fib Sum solution"
puts fibsum(1)
puts fibsum(2)
puts fibsum(3)
puts fibsum(4)
puts fibsum(5)
puts fibsum(6)
puts fibsum(7)
puts fibsum(25)

def morse(s)
  morse_dictionary = {
    "a" => ".-",
    "b" => "-...",
    "c" => "-.-.",
    "d" => "-..",
    "e" => ".",
    "f" => "..-.",
    "g" => "--.",
    "h" => "....",
    "i" => "..",
    "j" => ".---",
    "k" => "-.-",
    "l" => ".-..",
    "m" => "--",
    "n" => "-.",
    "o" => "---",
    "p" => ".--.",
    "q" => "--.-",
    "r" => ".-.",
    "s" => "...",
    "t" => "-",
    "u" => "..-",
    "v" => "...-",
    "w" => ".--",
    "x" => "-..-",
    "y" => "-.--",
    "z" => "--..",
    " " => " "
  }
  s.downcase!
  result = ""

  1.upto(s.size) do |i|
    result << morse_dictionary[s[i-1, 1]]
  end
  result
end

puts "Morse Code problem"
puts morse("a")
puts morse("B")
puts morse("Hello World")