Here's a method that returns the range:
def my_range(a, b)
a = a.delete(" ") # remove all spaces from string
b = b.delete(" ")
a, b = b, a if a.to_i > b.to_i # a is always smaller than b
ai, bi = a.to_i, b.to_i
pow = 1
while ai > 1
pow += 1
len = pow if ai % 10 != bi % 10
ai /= 10
bi /= 10
end
a + " - " + b[-len..-1]
end
puts my_range("0123456700", "0123456750") # 0123456700 - 750
puts my_range("0123456669", "0123456675") # 0123456669 - 675
puts my_range("0123400200", "0123500200") # 0123400200 - 3500200
puts my_range("012 345 678", "01 235 0521") # 012345678 - 350521