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class PalindromeFactors
attr_accessor :value, :factors
def initialize(num1, num2)
@value = num1 * num2
@factors = [[num1, num2]]
end
def add_factor(num1, num2)
@factors << [num1, num2] unless @factors.include? [num2, num1]
end
end
class Palindromes
def initialize(options)
max = options[:max_factor]
min = options[:min_factor] || 1
@range = min..max
@palindrome_factors = []
end
def is_palindrome?(num)
num.to_s == num.to_s.reverse
end
def generate
@range.each do |num1|
@range.each do |num2|
product = num1 * num2
if is_palindrome?(product)
already_found = @palindrome_factors.find{ |pf| pf.value == product }
if already_found
already_found.add_factor(num1, num2)
else
@palindrome_factors << PalindromeFactors.new(num1, num2)
end
end
end
end
end
def largest
@palindrome_factors.sort_by{ |pf| pf.value }.last
end
def smallest
@palindrome_factors.sort_by{ |pf| pf.value }.first
end
end
####### tests ###########
require 'fis/test'
extend Fis::Test
test 'largest_palindrome_from_single_digit_factors' do
palindromes = Palindromes.new(max_factor: 9)
palindromes.generate
largest = palindromes.largest
assert_equal 9, largest.value
assert [[[3, 3], [1, 9]], [[1, 9], [3, 3]]].include? largest.factors
end
test 'largest_palindrome_from_double_digit_factors' do
palindromes = Palindromes.new(max_factor: 99, min_factor: 10)
palindromes.generate
largest = palindromes.largest
assert_equal 9009, largest.value
assert_equal [[91, 99]], largest.factors
end
test 'smallest_palindrome_from_double_digit_factors' do
palindromes = Palindromes.new(max_factor: 99, min_factor: 10)
palindromes.generate
smallest = palindromes.smallest
assert_equal 121, smallest.value
assert_equal [[11, 11]], smallest.factors
end
test 'largest_palindrome_from_triple_digit_factors' do
palindromes = Palindromes.new(max_factor: 999, min_factor: 100)
palindromes.generate
largest = palindromes.largest
assert_equal 906609, largest.value
assert_equal [[913, 993]], largest.factors
end
test 'smallest_palindrome_from_triple_digit_factors' do
palindromes = Palindromes.new(max_factor: 999, min_factor: 100)
palindromes.generate
smallest = palindromes.smallest
assert_equal 10201, smallest.value
assert_equal [[101, 101]], smallest.factors
end
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