279. Perfect Squares

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 = 12
Output: 3
Explanation: 12 = 4 + 4 + 4.
```

Example 2:

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

Constraints:

• `1 <= n <= 104`

Rust Solution

``````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);
}
``````

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