positive Fibonacci sum

pos_fib_sum.txt

Each new term in the Fibonacci sequence is generated by adding the previous two terms. By starting with 1 and 2, the first 10 terms will be:

1, 2, 3, 5, 8, 13, 21, 34, 55, 89, ...

By considering the terms in the Fibonacci sequence whose values do not exceed four million, find the sum of the even-valued terms.

describe "fibonacci" do
  it "should return 10 for 8" do
    sum_even_fibonacci(8).should == 10
  end

  it "should return 1 as the first fibonacci term" do
    fib = FibonacciSequence.new
    fib.next.should == 1
  end

  it "should return 2 as the second fibonacci term" do
    fib = FibonacciSequence.new
    fib.next.next.should == 2
  end
end

class FibonacciSequence
  attr_reader :last, :current

  def initialize(seed1 = 0, seed2 = 1)
    @last = seed1
    @current = seed2
  end

  def next
    temp = @last
    @last = @current
    @current = @last + temp
    @current
  end
end

def sum_even_fibonacci(val)
  sum = 0
  fib = FibonacciSequence.new
  temp = fib.next
  while temp <= val do
    if temp % 2 == 0
      sum += temp
    end
    temp = fib.next
    icnt += 1
  end
  sum
end

puts sum_even_fibonacci(4000000)

#=> 4613732

terms = [1,2]
even_numbers = [terms.last]
begin
  next_t = terms.inject(:+)
  terms.push(next_t).shift
  even_numbers << terms[1] if terms[1] < 4_000_000 && terms[1] % 2 == 0
end while terms[1] < 4_000_000

puts even_numbers.inject(:+)

previous, current = 1, 2
sum = 0

while current <= 4_000_000
  sum += current if current.even?
  previous, current = current, previous + current
end

puts sum

fib_array = [1, 2]
current_num = 2
previous_num = 1
MAX_VALUE = 4_000_000

while fib_array.last.to_i < MAX_VALUE
  fib_array << (current_num + previous_num)
  previous_num = current_num
  current_num = fib_array.last
end
fib_array.pop if fib_array.last.to_i >= MAX_VALUE

# We now have good data to work with
answer = 0
fib_array.each do |i|
  answer += i if i % 2 == 0
end
# sum of all even fibonacci #s in the sequence from 1 to 4 mil
puts answer

Took Jake's code and made it easier to understand

terms = [1, 2]
even_numbers = [terms.last]
ceiling = 4_000_000

begin
  next_t = terms.inject(0) { |t, x| t + x }
  terms = [terms.last, next_t]
  if terms.last < ceiling && terms.last.even?
    even_numbers << terms.last
  end
end while terms.last < ceiling

puts even_numbers.inject(0) { |t, x| t + x }

def fibs
  Enumerator.new do |y|
    a, b = 0, 1
    loop do
      y << a
      a, b = b, a + b
    end
  end
end

puts fibs.take_while{|n| n <= 4E6}.select(&:even?).reduce(:+)