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202. Happy Number

Difficulty Topics

Description

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

Solution

happy-number.py
class Solution:
    def isHappy(self, n: int) -> bool:
        seen = set()

        while n != 1 and n not in seen:
            seen.add(n)
            curr = 0

            while n > 0:
                a, b = divmod(n, 10)
                curr += b * b
                n = a

            n = curr

        return n == 1