leetcode 202. Happy Number

发表于 | 分类于

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

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
class Solution(object):
    def isHappy(self, n):
        #解决周期循环的问题可以使用快慢指针
        def helper(n):
            result = 0
            while n != 0:
                result += pow(n%10,2)
                n = n//10
            return result
        
        r1 = helper(n)
        r2 = helper(r1)
        while r1 != 1:
            if r1 == r2:
                return False
            r1 = helper(r1)
            r2 = helper(helper(r2))
        return True