leetcode 202. Happy Number

leetcode 202. Happy Number

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LeetCode

描述

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

solution

思路：用一个集合记录每一步的数字，如果出现循环则退出

class Solution:
    def isHappy(self, n: int) -> bool:
        s=set()
        if n ==1:
            return True
        s.add(n)

        while n!=1 or n not in s:
            lst=list(str(n))
            n=sum([int(i)**2 for i in lst])
            if n in s:
                break;
            if n!=1:
                s.add(n)
            if n==1:
                return True

        return False