LC202 - Happy Number

Problem

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

Input: n = 19

Output: true

Explanation:

• 1^2 + 9^2 = 82

• 8^2 + 2^2 = 68

• 6^2 + 8^2 = 100

• 1^2 + 0^2 + 0^2 = 1

Solution

Time and space complexity is $O(n)$ since we use a set.

def isHappy(self, n: int) -> bool:
	Set = set()
	while n != 1:
		if n in Set:
			return False
		Set.add(n)
		n = sum([pow(int(i), 2) for i in str(n)])
	return True