public static void Visit(int row, int col, int n, Queue<int> queue, bool[] visited)
{
    if (row < 0 || col < 0 || row >= n || col >= n)
        return;
    int position = row * n + col;
    if (visited[position])
        return;
    visited[position] = true;
    queue.Enqueue(position);
}
public static int KnightHelper(int n, int i, int j)
{
    if (i == j)
    {
        return ((n - 1) % i == 0) ? (n - 1) / i : -1;
    }

    //try bfs
    bool[] visited = new bool[n * n];
    Queue<int> queue = new Queue<int>();
    int steps = 0;
    queue.Enqueue(0);
    while (queue.Count > 0)
    {
        int count = queue.Count();
        for (int m = 0; m < count; m++)
        {
            int position = queue.Dequeue();
            int row = (position / n);
            int col = (position % n);

            if (row == n - 1 && col == n - 1)
            {
                // Found solution.
                return steps;
            }

            Visit(row + i, col + j, n, queue, visited);
            Visit(row + i, col - j, n, queue, visited);
            Visit(row + j, col + i, n, queue, visited);
            Visit(row + j, col - i, n, queue, visited);
            Visit(row - i, col + j, n, queue, visited);
            Visit(row - i, col - j, n, queue, visited);
            Visit(row - j, col + i, n, queue, visited);
            Visit(row - j, col - i, n, queue, visited);
        }
        steps++;
    }
    return -1;
}