Diagonal Traverse
<p>Given an <code>m x n</code> matrix <code>mat</code>, return <em>an array of all the elements of the array in a diagonal order</em>.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>
<img alt="" src="https://fastly.jsdelivr.net/gh/doocs/leetcode@main/solution/0400-0499/0498.Diagonal%20Traverse/images/diag1-grid.jpg" style="width: 334px; height: 334px;" />
<pre>
<strong>Input:</strong> mat = [[1,2,3],[4,5,6],[7,8,9]]
<strong>Output:</strong> [1,2,4,7,5,3,6,8,9]
</pre>

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

<pre>
<strong>Input:</strong> mat = [[1,2],[3,4]]
<strong>Output:</strong> [1,2,3,4]
</pre>

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

<ul>
	<li><code>m == mat.length</code></li>
	<li><code>n == mat[i].length</code></li>
	<li><code>1 &lt;= m, n &lt;= 10<sup>4</sup></code></li>
	<li><code>1 &lt;= m * n &lt;= 10<sup>4</sup></code></li>
	<li><code>-10<sup>5</sup> &lt;= mat[i][j] &lt;= 10<sup>5</sup></code></li>
</ul>
Array; Matrix; Simulation
impl Solution {
    pub fn find_diagonal_order(mat: Vec<Vec<i32>>) -> Vec<i32> {
        let (m, n) = (mat.len(), mat[0].len());
        let (mut i, mut j) = (0, 0);
        (0..m * n)
            .map(|_| {
                let res = mat[i][j];
                if (i + j) % 2 == 0 {
                    if j == n - 1 {
                        i += 1;
                    } else if i == 0 {
                        j += 1;
                    } else {
                        i -= 1;
                        j += 1;
                    }
                } else {
                    if i == m - 1 {
                        j += 1;
                    } else if j == 0 {
                        i += 1;
                    } else {
                        i += 1;
                        j -= 1;
                    }
                }
                res
            })
            .collect()
    }
}
