- 题目提供者 FarmerJohn2
- 评测方式 云端评测
- 标签 凸包 数论,数学 素数判断,质数,筛法 USACO 2008 高性能
- 难度 省选/NOI-
- 时空限制 1000ms / 128MB
Farmer John has purchased N (5 <= N <= 250) fence posts in order to build a very nice-looking fence. Everyone knows the best fences are convex polygons where fence posts form vertices of a polygon. The pasture is represented as a rectilinear grid; fencepost i is at integer coordinates (x_i, y_i) (1 <= x_i <= 1,000; 1 <= y_i <= 1000).
Given the locations of N fence posts (which, intriguingly, feature no set of three points which are collinear), what is the largest number of fence posts FJ can use to create a fence that is convex?
For test cases worth 45% of the points for this problem, N <= 65.
Time limit: 1.2 seconds
* Line 1: A single integer: N
* Lines 2..N+1: Line i+1 describes fence post i's location with two space-separated integers: x_i and y_i输出格式：
* Line 1: A single integer, the maximum possible number of fence posts that form a convex polygon.
A square with two points inside.
The largest convex polygon is the pentagon (2,3), (3,2), (5,1), (5,5), (1,5).