Problem 2: You are running an art museum. There is a long hallway with k paintings on the wall. The locations of the paintings are l1,...,lk. These locations are real numbers, but not necessarily integers. You can place guards at locations in the hallway, and a guard can protect all paintings within 1 unit of distance from his location. The guards can be placed at any location, not just a location where there is a painting. Design a greedy algorithm to determine the minimum number of guards needed to protect all paintings.