说明：  某石油公司计划建造一条由东向西的主输油管道，这条管道要穿过n口油井的油田，每口油井通过一条次管道沿最短路径（或南或北）直接与主管道相连。就n口油井分布的一般位置，试确定主管道位置，使得各油井到主管道的输油管道长度总和达到最小。并验证可在线性时间内确定主管道的最优位置。
(An oil company plans to build a from east to west of the main oil pipeline, this pipeline to pass through n wells of oil fields, oil wells in every through a second pipeline along the shortest path (or South or North) directly connected with the competent Road. Wells on the n distribution of the general location, test to determine the competent Road location, making the well-to-charge of Road to minimize the sum of the length of pipeline. And verify that the linear time can be in charge of Road to determine the optimal location.)