Aaron Yodaiken - 8 months ago 36

Ruby 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-ishâ€”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

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.

As demas' has posted a solution, here's a cleaned up version:

```
class Fibo
class << self
include Enumerable
def each
return to_enum unless block_given?
a = 0; b = 1
loop do
a, b = b, a + b
yield a
end
end
end
end
puts Fibo.take_while { |i| i < 4000000 }.
select(&:even?).
inject(:+)
```