【leetcode】Happy Number

題目簡述

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: 19 is a happy number

12 + 92 = 82
82 + 22 = 68
62 + 82 = 100
12 + 02 + 02 = 1

解題思路

按照題目來就好，注意只有以1截止才happy，開始理解錯了

class Solution:
    # @param {integer} n
    # @return {boolean}
    def isHappy(self, n):
        a = []
        #res = 0
        while True:
            res = 0
            for i in str(n):
                res += int(i) ** 2
            if res == 1:
                return True
            elif len(a) > 1 and res == a[-1]:
                return False
            elif res in a:
                return False
            else:
                a.append(res)
                n = res