public static int hackerlandRadioTransmitters(List<int> houses, int range)
{
    houses.Sort();
    
    int transmittersCount = 0;
    int i = 0;
    
    while (i < houses.Count)
    {
        transmittersCount++;
        
        // Take the first house. 
        int left = houses[i];
        int mid = left + range;
        
        // Find the first house out of range, put a transmitter 1 house before there.
        while (i < houses.Count && houses[i] <= mid)
        {
            i++;
        }
        
        mid = houses[i-1];
        int right = mid + range;
        
        // Find the first house out of range. Repeat.
        while (i < houses.Count && houses[i] <= right)
        {
            i++;
        }
    }
    
    return transmittersCount;
}