Leetcode: Happy Number

最新推荐文章于 2017-03-12 21:25:37 发布

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最新推荐文章于 2017-03-12 21:25:37 发布

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本文介绍了一种算法，用于确定一个数字是否为快乐数。快乐数定义为通过将数字转换为其各个位数的平方和，重复此过程直到达到1或进入循环不包含1的周期。本文提供了实现这一概念的代码示例。

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Question

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
Credits:
Special thanks to @mithmatt and @ts for adding this problem and creating all test cases.

Solution

Analysis

How to determine whether it comes into cycle ? using hashset

Code

class Solution(object):
    def isHappy(self, n):
        """
        :type n: int
        :rtype: bool
        """

        hashset = set([])

        while True:
            n = list(str(n))
            n = [int(elem)**2 for elem in n]

            n = sum(n)
            if n==1:
                return True
            else:
                if n in hashset:
                    return False
                else:
                    hashset.add(n)