LeetCode202. Happy Number

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

---

思路:主要就是写一个循环,把数字转为字符串,再将每个数字平方后相加,构成新的数字.

至于判断是否有循环可以将每个生成的数字存在一个数组里,然后每次判断新生成的数字是否已经存在数组中.

class Solution(object):
    def isHappy(self, n):
        """
        :type n: int
        :rtype: bool
        """
        num=[]
        while(n!=1):

            sum = 0
            strs = str(n)
            for i in strs:
                sum += pow(int(i), 2)
            n = sum
            
            if n in num:
                return False
            else:
                num.append(n)

        return True

同时也发现其实每次出现循环都是从4开始,所以也可以直接判断.

class Solution(object):
    def isHappy(self, n):
        """
        :type n: int
        :rtype: bool
        """
        while(n!=1):
            
            if n == 4:
                return False

            sum = 0
            strs = str(n)
            for i in strs:
                sum += pow(int(i), 2)
            n = sum

        return True