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# rootulp's solution

## to Pythagorean Triplet in the Ruby Track

Published at Jul 13 2018 · 0 comments
Instructions
Test suite
Solution

#### Note:

This solution was written on an old version of Exercism. The tests below might not correspond to the solution code, and the exercise may have changed since this code was written.

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 a * b * c.

For installation and learning resources, refer to the exercism help 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 [3840], 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
end``````
``````# Pythagorean Theorem
# a**2 + b**2 = c**2

# Euclid's Formula
# (m**2 - n**2) + (2mn) = (m**2 + n**2)

require 'set'

# Triplet
class Triplet
attr_reader :a, :b, :c, :sides
def initialize(a, b, c)
@a = a
@b = b
@c = c
@sides = Set.new [a, b, c]
end

def sum
sides.reduce(:+)
end

def product
sides.reduce(:*)
end

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

def self.where(constraints = {})
min_factor = constraints.fetch(:min_factor, 1)
max_factor = constraints.fetch(:max_factor)
sum = constraints.fetch(:sum, nil)

find_triplets(min_factor, max_factor, sum)
end

def self.find_triplets(min_factor, max_factor, sum)
triplets = []
(min_factor..max_factor).to_a.combination(3).each do |a, b, c|
triplets << Triplet.new(a, b, c) if valid?(Triplet.new(a, b, c), sum)
end
triplets
end

def self.valid?(triplet, sum)
valid_sum?(triplet, sum) && valid_pythagorean?(triplet)
end

def self.valid_sum?(triplet, sum)
return true if sum.nil?
sum == triplet.sum
end

def self.valid_pythagorean?(triplet)
triplet.pythagorean?
end
end``````

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