Commit be361e8

@@ -0,0 +1,51 @@
+require 'prime'
+
+#The prime factors of 13195 are 5, 7, 13 and 29.
+
+#What is the largest prime factor of the number 600851475143 ?
+class OptimusPrime
+  def factors_of(number)
+    return [] if number == 1
+    lowest_prime = 1
+    each do |prime|
+      if number % prime == 0
+        lowest_prime = prime
+        break
+      end
+    end
+    ([lowest_prime] + factors_of(number / lowest_prime)).flatten
+  end
+
+  private
+
+  def each(&block)
+    Prime.each(&block)
+  end
+end
+describe 'problem three' do
+  subject { OptimusPrime.new }
+
+  it 'returns prime factorization' do
+    expect(subject.factors_of(13195)).to match_array([5, 7, 13, 29])
+  end
+
+  it 'returns the answer' do
+    expect(subject.factors_of(600851475143)).to match_array([71, 839, 1471, 6857])
+  end
+
+  it 'returns the answer to 65' do
+    expect(subject.factors_of(65)).to match_array([5, 13])
+  end
+
+  it 'returns the answer to 38' do
+    expect(subject.factors_of(38)).to match_array([2, 19])
+  end
+
+  it 'returns the answer to 48' do
+    expect(subject.factors_of(48)).to match_array([2, 2, 2, 2, 3])
+  end
+
+  it 'returns the answer to 64' do
+    expect(subject.factors_of(64)).to match_array([2, 2, 2, 2, 2, 2])
+  end
+end