PrimeFactors Kata Second iteration

prime_factors_2_spec.rb

module PrimeFactors
  def decompose(number)
    if number <= 3
      [number]
    else
      prime_factors = []
      (2..number / 2).each do |prime|
        while(number % prime).zero? do
          number = number / prime
          prime_factors << prime
        end
      end
      prime_factors
    end
  end
end

describe PrimeFactors do
  include PrimeFactors

  it "returns the factor 1 for 1" do
    decompose(1).should == [1]
  end

  it "returns the factor 2 for 2" do
    decompose(2).should == [2]
  end
  
  it "returns the factor 3 for 3" do
    decompose(3).should == [3]
  end

  it "returns the factors 2,2 for 4" do
    decompose(4).should == [2,2]
  end

  it "returns the factor 5 for 5" do
    decompose(5).should == [5]
  end

  it "returns the factors 2,3 for 6" do
    decompose(6).should == [2,3]
  end

  it "returns the factors 2,2,2 for 8" do
    decompose(8).should == [2,2,2]
  end

  it "returns the factors 2,2,3,5,7 for 420" do
    decompose(420).should == [2,2,3,5,7]
  end
end

Thats a nice way of doing it.. The tests read much nicer.

Yeah I thought about this problem with the number itself being prime and bigger 4 in bed..

I think it need a is_prime? method or so..

The main problem of this is really writing the right tests..

Here on line 21ff. Is 1 a prime factor of 1?

- Robert Curth [2012-07-04]: Here on line 21ff. Is 1 a prime factor of 1? In my book 1 is prime... ## "It's all part of my Can't-Do approach to life." Wally

A prime number (or a prime) is a natural number greater than 1 that has no positive divisors other than 1 and itself.

http://en.wikipedia.org/wiki/Prime_number

Here is the link to project euler btw..

http://projecteuler.net/problems