gistfile1.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.
#
def problem_2_algorithm input
  penultimate, last = [1, 2]
  sum = 0
  while last < input do
    next_value = penultimate + last
    if last.even?
      sum += last
    end
    penultimate = last
    last = next_value
  end
  sum
end

describe 'problem_2_algorithm' do
  it 'should return 44 with an input value of 100' do
    answer = problem_2_algorithm 100
    answer.should == 44
  end

  it 'should return the answer when the input value is 4,000,000' do
    answer = problem_2_algorithm 4000000
    puts answer
  end
end