HDOJ 1348 基本二维凸包问题

这次写的凸包用的是Graham scan算法

就数据结构上只是简单地运用了一个栈

#include<stdio.h>
#include<cmath>
#include<algorithm>
//#define LOCAL
using namespace std;
const int max1=1000;
typedef struct point
{
    int x;
    int y;
}point;
int cp(point a,point b,point c)
{
    c.x-=a.x;
    c.y-=a.y;
    b.x-=a.x;
    b.y-=a.y;
    return (b.x*c.y-b.y*c.x)>0;
}
int cmp(point a,point b)
{
    if(a.y!=b.y) return a.y<b.y;
     else return a.x<b.x;
}
double len(point a,point b)
{
    return sqrt((a.x-b.x)*(a.x-b.x)*1.0+(a.y-b.y)*(a.y-b.y)*1.0);
}
int main()
{
    #ifdef LOCAL
      freopen("data.in","r",stdin);
    #endif // LOCAL
    int t;
    point a1[max1+5],a2[max1+5];
    int N,L;
    int top,mtop,i;
    double ans;
    scanf("%d",&t);
    while(t--)
    {
        ans=0;
        scanf("%d%d",&N,&L);
        for(i=0;i<N;i++) scanf("%d%d",&a1[i].x,&a1[i].y);
        sort(a1,a1+N,cmp);
        a2[0]=a1[0];
        for(i=1,top=0;i<N;i++)//寻找最低点到最高点的右凸包
        {
            while(top!=0&&!cp(a2[top-1],a2[top],a1[i]))//在这里如果两条向量在同一条直线上的话(即CP==0)，就将a2【top】弹出
                //换成距离更远的点

                top--;
            a2[++top]=a1[i];
        }
        a2[++top]=a1[N-1];
        mtop=top;
        //for(i=0;i<top;i++) printf("%d %d\n",a2[i].x,a2[i].y);
        for(i=N-2;i>=0;i--)//寻找最低点到最高点的左凸包
        {
            while(top!=mtop&&!cp(a2[top-1],a2[top],a1[i]))
                top--;
            a2[++top]=a1[i];
        }
        for(i=0;i<top;i++)
        {
            ans+=len(a2[i],a2[(i+1)%top]);
        }
        ans+=2*L*3.14159;
        printf("%.0lf\n",ans);//四舍五入就行
        if(t!=0) printf("\n");
    }
    return 0;
}