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Happy Number

Problem Statement​

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.

Leetcode Link

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

Code​

Python Code

class Solution:
    def isHappy(self, n):
        mem = set()
        while n != 1:
            n = sum([int(i) ** 2 for i in str(n)])
            if n in mem:
                return False
            else:
                mem.add(n)
        else:
            return True