public static int hackerlandRadioTransmitters(List<Integer> x, int k) {
    // Write your code here
        if(x.size() < 1)
            return 0;
            
        int maxInd = x.stream().max(Comparator.comparingInt(Integer::intValue)).get();
        int minInd = x.stream().min(Comparator.comparingInt(Integer::intValue)).get();
        
        Set<Integer> houseIndex = new HashSet<>(x);
        int count = 0;
        int currentInd = minInd;
        while(currentInd <= maxInd) {
            if(houseIndex.contains(currentInd)) {
                count++;
                for(int i = k; i >= 0; i--) { // look for farthest house in range for radio installation 
                    if(houseIndex.contains(currentInd + i)) {
                        currentInd += i; //here radio installed
                        break;
                    }
                }
                currentInd += k;// till this range coverage is available
            }
            currentInd++; // move to find next house for coverage
        }
        return count;
    }

def hackerlandRadioTransmitters(x, k):
    size = len(x)
    if size == 1:
        return 1
        
    x.sort()
    num = 0
    i = 0
    while i < size:
        # mark the furthest location within the coverage at current i
        loc = x[i] + k
   
        # move to the furthest house within the range and set transmitter
        while i < size and x[i] <= loc:
            i += 1
        i -= 1
        num += 1
        
        # make the furthest location within the coverage at current i
        loc = x[i] + k
        
        # move to the first house outside the coverage
        while i < size and x[i] <= loc:
            i += 1
        
    return num

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;

Single Pass One Line 

def hackerlandRadioTransmitters(x: Array[Int], k: Int): Int = 
    x.foldLeft((-1,-1,-1)) {
      case ((-1,-1,-1),_) => 
        x.sortInPlace
        (1,x(0),x(0)+k)
      case ((i,l,r),house) if house - k <= l => 
          (i,l,house+k)           
      case ((i,l,r),house) if house > r => 
          (i+1,house,house+k)
      case acc => acc._1
      }._1