euler

require 'active_support/core_ext/enumerable'
require 'pry'
class ProjectEuler
  
  attr_accessor :hash, :array

  def initialize( args = {} )
    self.hash     = {}
    self.array    = []
  end

  def three_and_five
    # If we list all the natural numbers below 10 that are multiples of 3 or 5, we get 3, 5, 6 and 9. The sum of these multiples is 23.
    # Find the sum of all the multiples of 3 or 5 below 1000.
    ( 1..999 ).each do |n|
      next unless n % 3 == 0 || n % 5 == 0 
      array.push n
    end
    array.sum
  end
  
  def even_fibonacci_numbers
    # 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.
    array = [ 1, 2 ]
    past    = 1
    present = 2
    loop_through = true
    while loop_through do
      array.push( past + present )
      past          = present
      present       = array.last
      loop_through = false if ( past + present ) > 4000000
    end
    array.select{ |n| n % 2 == 0 }.sum
  end

  def largest_prime_factor
    # The prime factors of 13195 are 5, 7, 13 and 29.
    # What is the largest prime factor of the number 600851475143 ?
    check_again = lambda{ |n| }
    number = 600851475143
    hash = {
      number => { }
    }
    (2..( number / 2 ) ).each do |n|
      hash[ number ][ number / n ] = {}  if number % n == 0
    end
  end

  
end