0202-happy-number.rb

# frozen_string_literal: true

# 202. Happy Number
# https://leetcode.com/problems/happy-number

=begin

Write an algorithm to determine if a number n is happy.

A happy number is a number defined by the following process:

Starting with any positive integer, replace the number by the sum of the squares of its digits.
Repeat the process until the number equals 1 (where it will stay), or it loops endlessly in a cycle which does not include 1.
Those numbers for which this process ends in 1 are happy.
Return true if n is a happy number, and false if not.


### Example 1:
Input: n = 19
Output: true
Explanation:
12 + 92 = 82
82 + 22 = 68
62 + 82 = 100
12 + 02 + 02 = 1

### Example 2:
Input: n = 2
Output: false

### Constraints:
* 1 <= n <= 231 - 1

=end

# @param {Integer} n
# @return {Boolean}
def is_happy(n)
  touched = []
  res = n

  loop do
    res = res.digits.sum { |el| el * el }

    return false if touched.include?(res)
    return true if res == 1

    touched << res
  end
end

# **************** #
#       TEST       #
# **************** #

require "test/unit"
class Test_is_happy < Test::Unit::TestCase
  def test_
    assert_equal true, is_happy(19)
    assert_equal false, is_happy(2)
  end
end