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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
it "solves the problem" do
subject = NaturalNumbers.new(100)
expect(subject.difference).to eql(25164150)
end
end
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