<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://assets.leetcode.com/uploads/2021/04/10/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>

class Solution:
    def findDiagonalOrder(self, mat: List[List[int]]) -> List[int]:
        
        m = len(mat)
        n = len(mat[0])

        direction = [(-1, 1), (1, -1)]
        direction_idx = 0
        ans = []
        row = 0
        col = 0
       
        while len(ans) != m * n:

            ans.append(mat[row][col])
            delta_x, delta_y = direction[direction_idx]
            if direction_idx % 2 == 0:
                if col == n - 1:
                    row += 1
                    direction_idx = (direction_idx + 1) % 2
                elif row == 0:
                    direction_idx = (direction_idx + 1) % 2
                    col += 1
                else:
                    row += delta_x
                    col += delta_y
            else:
                if row == m - 1:
                    direction_idx = (direction_idx + 1) % 2
                    col += 1
                elif col == 0:
                    direction_idx = (direction_idx + 1) % 2
                    row += 1
                else:
                    row += delta_x
                    col += delta_y

        return ans
18900