Let's consider a long, straight country road with n houses scattered very sparsely along it. We can picture this road as a long line segment with an eastern endpoint and a western endpoint. Let di be the distance of the i-th house from the eastern endpoint. We are given as input di, for all . Further, let’s suppose that despite the bucolic setting, the residents of all these houses are avid cell phone users. You want to place cell phone base stations at certain points along the road, so that every house is within four miles of one of the base stations. Give an efficient algorithm that achieves this goal, using as few base stations as possible. Identify the complexity of your algorithm.