凸包模版和博客

http://blog.csdn.net/nyist_tc_lyq/article/details/74776760

http://blog.csdn.net/bone_ace/article/details/46239187

http://www.cnblogs.com/Booble/archive/2011/02/28/1967179.html

#include<bits/stdc++.h>
using namespace std;
struct Z
{
    double x,y;
} z[1000],p[1000];
//距离
double dis(Z a,Z b)
{
    double d=(a.x-b.x)*(a.x-b.x)+(a.y-b.y)*(a.y-b.y);
    return d;
}
//叉积
double mm(Z a,Z b,Z c)
{
    return (b.x-a.x)*(c.y-a.y)-(c.x-a.x)*(b.y-a.y);
}
//级角排序
int cmp(Z a,Z b)
{
    double x=mm(a,b,z[0]);
    if(x>0||(x==0&&dis(a,z[0])<dis(b,z[0])))
        return 1;
    return 0;
}
//输出排序
int cmpp(Z a,Z b)
{
    if(a.x!=b.x)
        return a.x<b.x;
    else return a.y<b.y;
}
int main()
{
    int  t;
    cin>>t;
    while(t--)
    {
        int m;
        cin>>m;
        int w=m;
        while(w--)
        {
            cin>>z[w].x>>z[w].y;
        }
//Graham扫描法
        int k=0;
        for(int i=0; i<m; i++)
        {
            if(z[i].y<z[k].y||(z[i].y==z[k].y&&z[i].x<z[k].x))k=i;
        }
        swap(z[0],z[k]);
        sort(z+1,z+m,cmp);
        int top=2;
        p[0]=z[0];
        p[1]=z[1];
        for(int i=2; i<m; i++)
        {
            while(top>1&&mm(p[top-1],p[top-2],z[i])>=0)
            {
                top--;
            }
            p[top++]=z[i];
        }
//输出要求
        sort(p,p+top,cmpp);
        cout<<top<<endl;
        for(int i=0; i<top; i++)
        {
            cout<<p[i].x<<" "<<p[i].y<<endl;;
        }
    }
}