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*.

**Example 1:**

Input:n = 19Output:trueExplanation:1^{2}+ 9^{2}= 82 8^{2}+ 2^{2}= 68 6^{2}+ 8^{2}= 100 1^{2}+ 0^{2}+ 0^{2}= 1

**Example 2:**

Input:n = 2Output:false

**Constraints:**

`1 <= n <= 2`

^{31}- 1

```
struct Solution;
impl Solution {
fn digit_square_sum(mut x: i32) -> i32 {
let mut sum = 0;
while x > 0 {
let tmp = x % 10;
sum += tmp * tmp;
x /= 10;
}
sum
}
fn is_happy(n: i32) -> bool {
let mut slow = n;
let mut fast = n;
loop {
slow = Self::digit_square_sum(slow);
fast = Self::digit_square_sum(fast);
fast = Self::digit_square_sum(fast);
if slow == fast {
break;
}
}
slow == 1
}
}
#[test]
fn test() {
assert_eq!(Solution::is_happy(19), true);
}
```