Write an algorithm to determine if a number `n` is happy.

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.

Example 1:

```Input: n = 19
Output: true
Explanation:
12 + 92 = 82
82 + 22 = 68
62 + 82 = 100
12 + 02 + 02 = 1
```

Example 2:

```Input: n = 2
Output: false
```

Constraints:

• `1 <= n <= 231 - 1`

Idea:

create a function to calculate the sum of the squares of its digits.

use fast and slow pointers traversal concept (the other one execute function twice) to check if they can reach 1 (means it is happy number)

Solution:

``````/**
* @param {number} n
* @return {boolean}
*/
var isHappy = function(n) {
let slow = n;
let fast = n;

do {
slow = squareSum(slow);
fast = squareSum(squareSum(fast));
} while (slow !== fast);

return fast === 1;
};

var squareSum = function(n) {
let sum = 0;
while(n) {
sum += (n % 10) * (n % 10);
n = parseInt(n / 10);
}
return sum;
};``````