Perfect Squares
<p>Given an integer <code>n</code>, return <em>the least number of perfect square numbers that sum to</em> <code>n</code>.</p>

<p>A <strong>perfect square</strong> is an integer that is the square of an integer; in other words, it is the product of some integer with itself. For example, <code>1</code>, <code>4</code>, <code>9</code>, and <code>16</code> are perfect squares while <code>3</code> and <code>11</code> are not.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>

<pre>
<strong>Input:</strong> n = 12
<strong>Output:</strong> 3
<strong>Explanation:</strong> 12 = 4 + 4 + 4.
</pre>

<p><strong class="example">Example 2:</strong></p>

<pre>
<strong>Input:</strong> n = 13
<strong>Output:</strong> 2
<strong>Explanation:</strong> 13 = 4 + 9.
</pre>

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li><code>1 &lt;= n &lt;= 10<sup>4</sup></code></li>
</ul>
Breadth-First Search; Math; Dynamic Programming
impl Solution {
    pub fn num_squares(n: i32) -> i32 {
        let (row, col) = ((n as f32).sqrt().floor() as usize, n as usize);
        let mut dp = vec![vec![i32::MAX; col + 1]; row + 1];
        dp[0][0] = 0;
        for i in 1..=row {
            for j in 0..=col {
                dp[i][j] = dp[i - 1][j];
                if j >= i * i {
                    dp[i][j] = std::cmp::min(dp[i][j], dp[i][j - i * i] + 1);
                }
            }
        }
        dp[row][col]
    }
}
