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.

**Solution:**

There's a endless loop means the result already appeared once. So just keep track all results.

```
class Solution {
func isHappy(_ n: Int) -> Bool {
var seen = Set<Int>()
var val = n
while !seen.contains(val) {
seen.insert(val)
val = val.modified()
if val == 1 {
return true
}
}
return false
}
}
extension Int {
func modified() -> Int {
var number = self
var result: Int = 0
while number > 0 {
result += (Int(pow(Double(number % 10), 2)))
number = number / 10
}
return result
}
}
```