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# Happy Number

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, 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.

Return True if `n` is a happy number, and False if not.

**Example:** 

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

```java
class Solution {
    public int digitSquareSum(int n) {
        int sum = 0;
        while (n > 0) {
            sum += (n % 10) * (n % 10);
            n /= 10;
        }
        return sum;
    }

    // Floyd Cycle detection algorithm
    public boolean isHappy(int n) {
        int slow, fast;
        slow = fast = n;
        do {
            slow = digitSquareSum(slow);
            fast = digitSquareSum(fast);
            fast = digitSquareSum(fast);
            if (fast == 1)
                return true;
        } while (slow != fast);
        return false;
    }
}
```