more ruby way of doing project euler #2

Question

I'm trying to learn Ruby, and am going through some of the Project Euler problems. I solved problem number two as such:

def fib(n)
  return n if n < 2
  vals = [0, 1]
  n.times do
    vals.push(vals[-1]+vals[-2])
  end
  return vals.last
end
i = 1
s = 0
while((v = fib(i)) < 4_000_000)
  s+=v if v%2==0
  i+=1
end
puts s

While that works, it seems not very ruby-ish—I couldn't come up with any good purely Ruby answer like I could with the first one ( puts (0..999).inject{ |sum, n| n%3==0||n%5==0 ? sum : sum+n }).

Answer 1

For a nice solution, why don't you create a Fibonacci number generator, like Prime or the Triangular example I gave here.

From this, you can use the nice Enumerable methods to handle the problem. You might want to wonder if there is any pattern to the even Fibonacci numbers too.

Edit your question to post your solution...

Note: there are more efficient ways than enumerating them, but they require more math, won't be as clear as this and would only shine if the 4 million was much higher.

Answer 2

That's my approach. I know it can be less lines of code, but maybe you can take something from it.

class Fib
  def first
    @p0 = 0
    @p1 = 1
    1
  end
  def next
    r = 
      if @p1 == 1
        2
      else
        @p0 + @p1
      end
    @p0 = @p1
    @p1 = r
    r
  end
end

c = Fib.new
f = c.first
r = 0
while (f=c.next) < 4_000_000
  r += f if f%2==0
end
puts r