#Description
按顺序给你N个点 问是否是凸包
#Algorithm
对每三个点用ccw函数判断一下,
看是不是同向
还要判断后面的点和前面的组成的情况,我是把前面的点加到后面处理的
#Code
#include <cstdio>
#include <iostream>
using namespace std;
const int maxn = 1e8;
struct P
{
int x, y;
};
int ccw(P a, P b, P c)
{
return (b.x - a.x) * (c.y - a.y) - (c.x - a.x) * (b.y - a.y);
}
P a[maxn];
int main()
{
for (;;)
{
int n;
cin >> n;
if (n == 0) break;
for (int i = 0; i < n; i++)
cin >> a[i].x >> a[i].y;
bool flag = true;
a[n++] = a[0];
a[n++] = a[1];
for (int i = 0; i < n - 3; i++)
if (ccw(a[i], a[i + 1], a[i + 2]) * ccw(a[i + 1], a[i + 2], a[i + 3]) < 0)
{
flag = false;
break;
}
if (flag) puts("convex"); else puts("concave");
}
}