Given an integer `n`

, return *the least number of perfect square numbers that sum to* `n`

.

A **perfect square** is an integer that is the square of an integer; in other words, it is the product of some integer with itself. For example, `1`

, `4`

, `9`

, and `16`

are perfect squares while `3`

and `11`

are not.

**Example 1:**

Input:n = 12Output:3Explanation:12 = 4 + 4 + 4.

**Example 2:**

Input:n = 13Output:2Explanation:13 = 4 + 9.

**Constraints:**

`1 <= n <= 10`

^{4}

```
struct Solution;
impl Solution {
fn num_squares(n: i32) -> i32 {
let n = n as usize;
let mut dp = vec![std::usize::MAX; n + 1];
dp[0] = 0;
for i in 1..=n {
let mut j = 1;
while j * j <= i {
dp[i] = dp[i].min(dp[i - j * j] + 1);
j += 1;
}
}
dp[n] as i32
}
}
#[test]
fn test() {
let n = 12;
let res = 3;
assert_eq!(Solution::num_squares(n), res);
let n = 13;
let res = 2;
assert_eq!(Solution::num_squares(n), res);
}
```