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
- 12 + 92 = 82,
- 82 + 22 = 68,
- 62 + 82 = 100,
- 12 + 02 + 02 = 1
思路：
若 n 为 1 ，则是 HappyNumber ，返回 true ；若不断循环，则不是 HappyNumber 。 所以关键在于如何判断是否进入循环。这里我采用的是将生成的新数存入 set 中，当 set 中已有这个数时，说明循环，返回 false 。
代码实现：
class Solution {
public:
bool isHappy(int n) {
unordered_set<int> aSet;
while(n>0){
if(n==1){
return true;
}
if(aSet.count(n)){
return false;
}
aSet.insert(n);
int temp=n;
int sum=0;
int b;
while(temp!=0){
b=temp%10;
sum+=b*b;
temp/=10;
}
n=sum;
sum=0;
}
return false;
}
};