public class Solution {
    public int[] FindDiagonalOrder(int[,] matrix) {
        var row = matrix.GetLength(0);
            var col = matrix.GetLength(1);

            var upBound = row - 1 + col - 1;

            var ary = new int[row * col];

            int i = 0;
            int j = 0;

            var index = 0;

            if (row == 1)
            {
                for (int m = 0; m < col; m++)
                {
                    ary[index++] = matrix[0, m];
                }
                return ary;
            }
            if (col == 1)
            {
                for (int m = 0; m < row; m++)
                {
                    ary[index++] = matrix[m, 0];
                }
                return ary;
            }

            var direction = true;//

            for (int k = 0; k <= upBound; k++)//对角线上的i，j之和
            {
                if (i == 0 && j == 0)
                {
                    ary[index++] = matrix[i, j];
                    j = 1;
                    continue;
                }
                //结束点
                if (i == row - 1 && j == col - 1)
                {
                    ary[index++] = matrix[i, j];
                    break;
                }
                var EndJ = Math.Min(i, col - 1);//0
                var EndI = Math.Min(j, row - 1);//1
                while (i + j == k)
                {
                    ary[index++] = matrix[i, j];
                    if ((direction && (j == 0 || i == row - 1)) || (!direction && (i == 0 || j == col - 1)))
                    {
                        if (direction)
                        {
                            i++;
                            if (i > row - 1)
                            {
                                i = row - 1;
                                j++;
                                if (j > col - 1)
                                {
                                    j = col - 1;
                                }
                            }
                        }
                        else
                        {
                            j++;
                            if (j > col - 1)
                            {
                                j = col - 1;
                                i++;
                                if (i > row - 1)
                                {
                                    i = row - 1;
                                }
                            }
                        }

                        direction = !direction;
                        continue;
                    }
                    if (direction)
                    {
                        i++;
                        if (i > row - 1)
                        {
                            i = row - 1;
                        }
                        j--;
                        if (j < 0)
                        {
                            j = 0;
                        }
                    }
                    else
                    {
                        j++;
                        if (j > col - 1)
                        {
                            j = col - 1;
                        }
                        i--;
                        if (i < 0)
                        {
                            i = 0;
                        }
                    }

                }
            }
            return ary;
    }
}