凸包模板

#include <iostream>#include<cstdio>#include<cstring>#include<algorithm>#include<cmath>using namespace std;typedef double PointType;struct point{    PointType x,y;    int num;};point data[1005],stack[1005],MinA;int top;PointType Direction(point pi,point pj,point pk) //判断向量PiPj在向量PiPk的顺逆时针方向 +顺-逆0共线{    return (pj.x-pi.x)*(pk.y-pi.y)-(pk.x-pi.x)*(pj.y-pi.y);}PointType Dis(point a,point b){    return sqrt((a.x-b.x)*(a.x-b.x)+(a.y-b.y)*(a.y-b.y));}bool cmp(point a,point b){    PointType k=Direction(MinA,a,b);    if(k>0) return 1;    if(k<0) return 0;    return Dis(MinA,a)>Dis(MinA,b);}void Graham_Scan(point *a,int numa){    for(int i=0; i<numa; i++)        if(a[i].y<a[0].y||(a[i].y==a[0].y&&a[i].x<a[0].x))            swap(a[i],a[0]);    MinA=a[0],top=0;    sort(a+1,a+numa,cmp);    stack[top++]=a[0],stack[top++]=a[1],stack[top++]=a[2];    for(int i=3; i<numa; i++)    {        while(Direction(stack[top-2],stack[top-1],a[i])<0&&top>=2)            top--;        stack[top++]=a[i];    }}int main(){    int n;    double r,pi=3.141592654;    while(~scanf("%d%lf",&n,&r))    {        double sum=0;        for(int i=0; i<n; i++)            scanf("%lf%lf",&data[i].x,&data[i].y);        Graham_Scan(data,n);        for(int i=1; i<top; i++)            sum+=Dis(stack[i],stack[i-1]);        sum+=Dis(stack[0],stack[top-1]);        sum+=pi*r*2;        printf("%.0fn",sum);    }    return 0;}