leetcode---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

class Solution {
public:
bool isHappy(int n) {
if(n < 1)
return false;
else if(n == 1)
return true;
set<int> s;
int sum = 0;
while(1)
{
sum = 0;
while(n)
{
int c = n % 10;
sum += c * c;
n /= 10;
}
n = sum;
if(sum == 1)
return true;
else if(sum < 1)
return false;
if(s.count(sum) == 0)
s.insert(sum);
else
return false;
}
}
};