void printShortestPath(int n, int i_start, int j_start, int i_end, int j_end) {
    std::vector<std::tuple<int, int, std::string>> direct = {{-2, -1, "UL"}, {-2, 1, "UR"}, {0, 2, "R"},{2, 1, "LR"},{2, -1, "LL"},{0, -2, "L"}};
    // Print the distance along with the sequence of moves.
   queue<std::tuple<int, int, std::string>> pq;
    vector<vector<bool>> vis(n, vector<bool>(n, false));
    vis[i_start][j_start] = true;
    // add start point
    int steps = 0;
    pq.emplace(i_start, j_start, string(""));
    int step = 0;
    while(!pq.empty()) {
        int size = pq.size();
        steps++;
        while (size--) {
           auto [r, c, path] = pq.front();
            pq.pop();
            // reach target node
            if (r == i_end && c == j_end) {
                cout << steps-1 << endl; 
                cout << path << endl;
                return;
            }
            for (const auto& [nb_r, nb_c, name]: direct) {
                int new_r = r + nb_r;
                int new_c = c + nb_c;
                // validate node
                if (new_r >= 0 && new_r <n && new_c>=0 && new_c <n && !vis[new_r][new_c]){
                    vis[new_r][new_c] = true;
                    pq.emplace(new_r, new_c, path + name + " ");
                    }
                }
            }
        } 
    // not found any path
    cout << "Impossible" << endl;
}