# Happy Number Problem & Solution

Write an algorithm to determine if a number `n`

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.
- 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.

Return true if `n`

is a happy number, and false if not.

See the happy number problem on LeetCode.

## C++ Solution

```
#pragma GCC optimize("Ofast")
#pragma GCC optimization("unroll-loops")
static const int _=[](){std::ios::sync_with_stdio(false);cin.tie(nullptr);cout.tie(nullptr);return 0;}();
class Solution {
public:
bool isHappy(int n) {
int slow = happy(n);
int fast = happy(slow);
while (slow != fast) {
slow = happy(slow);
fast = happy(happy(fast));
}
return slow == 1;
}
private:
int happy(int n) {
int sum = 0;
while (n > 0) {
sum += pow(n % 10, 2);
n /= 10;
}
return sum;
}
};
```