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;
    }