[LeetCode]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

1^2 + 9^2 = 82
8^2 + 2^2 = 68
6^2 + 8^2 = 100
1^2 + 0^2 + 0^2 = 1

题目大意:

编写一个算法判断某个数字是否是“快乐数”。

快乐数的定义过程如下:从任意一个正整数开始,将原数替换为其每一位的平方和,重复此过程直到数字=1(此时其值将不再变化),或者进入一个不包含1的无限循环。那些以1为过程终止的数字即为“快乐数”。

例如:19是一个快乐数,演算过程见题目描述。

解题思路:

模拟题,循环过程中用set记录每次得到的平方和

当出现非1的重复平方和时,返回False

否则,返回True

Python代码:

class Solution:
    # @param {integer} n
    # @return {boolean}
    def isHappy(self, n):
        numSet = set()
        while n != 1 and n not in numSet:
            numSet.add(n)
            sum = 0
            while n:
                digit = n % 10
                sum += digit * digit
                n /= 10
            n = sum
        return n == 1

 

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