Happy Number

题目描述

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: 19 is a happy number

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

解题方法

• 用一个hashmap记录出现过的数
• 如果新得到的结果已经出现过，说明进入了死循环
• 否则一直计算到结果为1

Solution

class Solution(object):
    def isHappy(self, n):
        """
        :type n: int
        :rtype: bool
        """
        if n == 0:
            return False
        dic = {}
        while n != 1:
            tmp = self.getSquareSum(n)
            if tmp in dic:
                return False
            else:
                dic[tmp] = True
            n = tmp
        return True

    def getSquareSum(self, n):
        result = 0
        while n:
            result += (n % 10) ** 2
            n /= 10
        return result

Reference