202. 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: 19 is a happy number

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

代码：

class Solution {public:    bool isHappy(int n) {        unordered_set<int> cache;   //用于记录中间过程计算的平方和        while(n!=1 && cache.find(n)==cache.end())//循环终止条件为最后记录的n=1（返回true）或者n与cache中记录的中间过程有重复的（返回false）        {            cache.insert(n);            int temp=0;            while(n!=0)            {                temp+=pow(n%10,2);                n=n/10;            }            n=temp;        }        if(n==1)            return true;        else            return false;    }};