202. Happy Number

Easy

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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

class Solution:
    def isHappy(self, n: int) -> bool:
        d = {}
        num = n
        while num != 1:
            if num not in d:
                d[num] = 1
            else:
                return False
            sum_ = 0
            for digit in str(num):
                sum_ += pow(int(digit), 2)
            num = sum_
        return True