it computes the sum of the squares and square of sums.

1 files changed, 56 insertions, 0 deletions

diff --git a/spec/euler/problem_six_spec.rb b/spec/euler/problem_six_spec.rb
new file mode 100644
index 0000000..d51e1f6
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+++ b/spec/euler/problem_six_spec.rb
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+require "spec_helper"
+
+describe "problem six" do
+  #Find the difference between the sum of the squares of the first one hundred natural numbers and the square of the sum.
+
+  class NaturalNumbers
+    include Enumerable
+    attr_reader :limit
+
+    def initialize(limit)
+      @limit = limit
+    end
+
+    def each
+      0.upto(limit) do |n|
+        yield n
+      end
+    end
+
+    def sum_of_squares
+      sum { |n| n*n }
+    end
+
+    def square_of_the_sum
+      result = sum
+      result * result
+    end
+
+    def difference
+      square_of_the_sum - sum_of_squares
+    end
+
+    private
+
+    def sum
+      inject(0) do |memo, n|
+        memo += block_given? ? yield(n) : n
+      end
+    end
+  end
+
+  it "returns the sum of first 10 natural numbers" do
+    subject = NaturalNumbers.new(10)
+    expect(subject.sum_of_squares()).to eql(385)
+  end
+
+  it "returns the square of the sum of the first 10 natural numbers" do
+    subject = NaturalNumbers.new(10)
+    expect(subject.square_of_the_sum()).to eql(3025)
+  end
+
+  it "returns the different between the sum of the squares and the square of the sum" do
+    subject = NaturalNumbers.new(10)
+    expect(subject.difference).to eql(2640)
+  end
+end