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