498. Diagonal Traverse

public class Solution
{
    public int[] FindDiagonalOrder(int[][] matrix)
    {
        // matrix dimensions
        int m = matrix.Length;
        int n = matrix[0].Length;

        // result array
        int[] result = new int[m * n];

        // index for the result array
        int index = 0;

        // temporary list to store diagonal elements
        List<int> diagonal = new List<int>();

        // loop through each diagonal starting from the top-left corner moving towards the right-bottom corner
        for (int diag = 0; diag < m + n - 1; ++diag)
        {
            // determine the starting row index for the current diagonal
            int row = diag < n ? 0 : diag - n + 1;

            // determine the starting column index for the current diagonal
            int col = diag < n ? diag : n - 1;

            // collect all the elements from the current diagonal
            while (row < m && col >= 0)
            {
                diagonal.Add(matrix[row][col]);
                ++row;
                --col;
            }

            // reverse the diagonal elements if we are in an even diagonal (starting counting from 0)
            if (diag % 2 == 0)
                diagonal.Reverse();

            // add the diagonal elements to the result array
            foreach (int element in diagonal)
                result[index++] = element;

            // clear the temporary diagonal list for the next iteration
            diagonal.Clear();
        }
        return result;
    }
}