构造凸包接口函数,传入原始点集大小n,点集p(p原有顺序被打乱!),返回凸包大小,凸包的点在convex中-Construct convex hull interface function, introduced the original point set size n, the point set p (p the original order has been disrupted!), Returns the size of the convex hull, convex hull of the points in the convex