Apartments CSES solving code https://cses.fi/problemset/task/1084

main.cpp

    while (t--)
    {
        int out = 0 , last = 0 ;
        dec (int , n  , m , k );
        array(int , dis , n );
        array(int , size , m);
        std :: sort (dis.begin() , dis.end());
        std :: sort (size.begin() , size.end());
        int ptr1 = 0 , ptr2 = 0  ;
            while (ptr2 < m && ptr1 < n) {
                {
                    //std :: cout << dis[ptr1] << " " << size [ptr2] << "\n";
                    if (std :: abs (dis[ptr1] - size [ptr2]) <= k )
                    {
                        ptr1 ++ ;
                        ptr2 ++ ;
                        out ++ ;
                    }
                    else {
                        if (dis[ptr1 ] < size[ptr2])
                            ptr1++;
                        else
                            ptr2 ++ ;
                    }
                }
            }

        p(out);
    }