LeetCode题解专栏：LeetCode题解
LeetCode 所有题目总结：LeetCode 所有题目总结

题目地址：Happy Number - LeetCode

Write an algorithm to determine if a number 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, and 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 numbers.

Example:

Input: 19
Output: true
Explanation: 
12 + 92 = 82
82 + 22 = 68
62 + 82 = 100
12 + 02 + 02 = 1

这道题目明显是数学题
Python解法如下：

class Solution:
    def isHappy(self, n: int) -> bool:
        s = set()
        while True:
            num = str(n)
            temp = 0
            for i in num:
                temp += int(i)**2
            if temp in s:
                return False
            elif temp == 1:
                return True
            else:
                s.add(temp)
                n = temp