 paulfioravanti's solution

to Pythagorean Triplet in the Ruby Track

Published at May 19 2019 · 0 comments
Instructions
Test suite
Solution

A Pythagorean triplet is a set of three natural numbers, {a, b, c}, for which,

a**2 + b**2 = c**2

and such that,

a < b < c

For example,

3**2 + 4**2 = 9 + 16 = 25 = 5**2.

Given an input integer N, find all Pythagorean triplets for which a + b + c = N.

For example, with N = 1000, there is exactly one Pythagorean triplet for which a + b + c = 1000: {200, 375, 425}.

For installation and learning resources, refer to the Ruby resources page.

For running the tests provided, you will need the Minitest gem. Open a terminal window and run the following command to install minitest:

gem install minitest

If you would like color output, you can require 'minitest/pride' in the test file, or note the alternative instruction, below, for running the test file.

Run the tests from the exercise directory using the following command:

ruby pythagorean_triplet_test.rb

To include color from the command line:

ruby -r minitest/pride pythagorean_triplet_test.rb

Source

Problem 9 at Project Euler http://projecteuler.net/problem=9

Submitting Incomplete Solutions

It's possible to submit an incomplete solution so you can see how others have completed the exercise.

pythagorean_triplet_test.rb

require 'minitest/autorun'
require_relative 'pythagorean_triplet'

class TripletTest < Minitest::Test
def test_sum
assert_equal 12, Triplet.new(3, 4, 5).sum
end

def test_product
skip
assert_equal 60, Triplet.new(3, 4, 5).product
end

def test_pythagorean
skip
assert Triplet.new(3, 4, 5).pythagorean?
end

def test_not_pythagorean
skip
refute Triplet.new(5, 6, 7).pythagorean?
end

def test_triplets_upto_10
skip
triplets = Triplet.where(max_factor: 10)
products = triplets.map(&:product).sort
assert_equal [60, 480], products
end

def test_triplets_from_11_upto_20
skip
triplets = Triplet.where(min_factor: 11, max_factor: 20)
products = triplets.map(&:product).sort
assert_equal , products
end

def test_triplets_where_sum_x
skip
triplets = Triplet.where(sum: 180, max_factor: 100)
products = triplets.map(&:product).sort
assert_equal [118_080, 168_480, 202_500], products
end

def test_where_sum_1000
skip
triplets = Triplet.where(sum: 1_000, min_factor: 200, max_factor: 425)
products = triplets.map(&:product)
assert_equal [31_875_000], products
end
end
class Triplet
NUM_SIDES = 3
private_constant :NUM_SIDES

def self.where(min_factor: 1, max_factor:, sum: nil)
(min_factor..max_factor)
.to_a
.combination(NUM_SIDES)
.with_object(sum)
end

def self.add_pythagorean_triplet(((a, b, c), sum), acc)
triplet = Triplet.new(a, b, c)
acc << triplet if pythagorean_triplet?(triplet, sum)
end

def self.pythagorean_triplet?(triplet, sum)
triplet.pythagorean? && (triplet.sum == sum || sum.nil?)
end
private_class_method :pythagorean_triplet?

def initialize(a_num, b_num, c_num)
@sides = [a_num, b_num, c_num].sort
@a, @b, @c = sides
end

def sum
sides.sum
end

def product
sides.reduce(&:*)
end

def pythagorean?
a**2 + b**2 == c**2
end

private

attr_reader :a, :b, :c, :sides
end