You've been hired by Telstra to set up mobile phone towers along a straight road in a rural area. There are n customers. Each customer's mobile device has a specific range in which it can send and receive signals to and from a tower. The goal is to ensure that each customer is within range of a tower while using as few towers as possible. More formally, each customer has an associated interval [?i ,ri ], where ?i and ri are positive integers (li ? ri ). The interval of a customer specifies the range of their mobile device. Serving customer i requires us to place a tower at a location x satisfying ?i ? x ? ri . A solution is a set L of tower locations and is feasible if for each customer i, there exists a location x ? L satisfying ?i ? x ? ri . We're interested in constructing the smallest set L that is feasible.

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