int hackerlandRadioTransmitters(vector<int> x, int k) {
    sort(x.begin(), x.end());
    int n_radios = 0;
    int N = x.size();
    int house = 0;
    int i = 0;
    while(i < N){
        house = x[i];  // radio installed here
        while(i < N && x[i] <= house + k){
            i ++;
        }
        n_radios ++;
        house = x[i-1];  // radio installed here
        while(i < N && x[i] <= house + k){
            i ++;
        }
    }
    return n_radios;