closest_pair

代码说明：

  分治法思想，求最邻近点对，考虑将所给的n个点的集合S分成2个子集S1和S2，每个子集中约有n/2个点，然后在每个子集中递归地求其最接近的点对(Divide and conquer ideas, find the nearest point to consider given the set S of n points into two subsets S1 and S2, each subset of about n/2 points, and then recursively find its focus in each sub-the closest point)