Mohsin Kaleem

I'm a developer

Happy Number

def sum_digits_squared(num)
  num.to_s
     .split('')
     .map { |i| i.to_i ** 2 }
     .reduce { |i, j| i + j }
end

def happy_num?(num)
  mem = []
  while num != 1
    return false if mem.include?(num)

    mem << num
    num = sum_digits_squared(num)
  end
  true
end

#Challenge

SourceLanguage
leetcoderuby

A happy number is a number which through the following process eventually converges to 1. We take the number and then square each digit of its representation and then sum them. If this process loops indefinitely then we do not have a happy number.

#Solution

Simply perform the desired operation until you converge at 1. The trick is detecting when you enter an infinite loop and accounting for it. In this case I track every number at each iteration and if I encounter the same number twice I conclude I've entered a loop and return false.

#Test Cases

using all happy numbers under 100.

happies = [1, 7, 10, 13, 19, 23, 28, 31, 32, 44, 49,
           68, 70, 79, 82, 86, 91, 94, 97, 100]

(2..100).each do |num|
  is_happy = happy_num?(num)
  if is_happy != happies.include?(num)
    if is_happy
      puts "FAILED: #{num} is happy when it shouldn't be"
    else
      puts "FAILED: #{num} is not happy when it should be"
    end
  end
end

# As with unix, silence is good 😄.