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require "spec_helper"
describe "problem nine" do
# A Pythagorean triplet is a set of three natural numbers, a < b < c, for which, a^2 + b^2 = c^2
# For example, 3^2 + 4^2 = 9 + 16 = 25 = 5^2.
# There exists exactly one Pythagorean triplet for which a + b + c = 1000.
# Find the product abc.
# a < b < c
# c^2 = a^2 + b^2
class PythagoreanTriplet
include Enumerable
attr_reader :max
def initialize(max = 1_000)
@max = max
end
def each(&block)
triplets.each(&block)
end
private
def triplets
Enumerator.new do |yielder|
(2..max).each do |m|
(1...m).each do |n|
# https://en.wikipedia.org/wiki/Pythagorean_triple#Proof_of_Euclid.27s_formula
a, b, c = m*m - n*n, 2*m*n, m*m + n*n
yielder.yield([a, b, c])
end
end
end
end
end
subject { PythagoreanTriplet.new }
it "returns the triplet for 25" do
expect(subject.first).to eql([3, 4, 5])
result = subject.find do |triplet|
(triplet.last * triplet.last) == 25
end
expect(result).to eql([3, 4, 5])
expect(subject).to include([3, 4, 5])
expect(subject).to include([5, 12, 13])
end
it "returns the triplet for 1000" do
result = subject.find do |triplet|
(triplet[0] + triplet[1] + triplet[2]) == 1_000
end
expect(result).to eql([375, 200, 425])
puts 375*200*425
end
end
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