二维凸包的板子

Posted 2021-01-30 ppprseter

二维凸包的板子

感觉没什么可说的，码风抄的孔老师的。

#include <cstdio>
#include <algorithm>
#include <cmath>
const int N=1e4+10;
#define Point Vector
const double eps=1e-8;
bool cmp(double a,double b){return fabs(a-b)<eps;}
struct Vector
{
    double x,y;
    Vector(){}
    Vector(double x,double y){this->x=x,this->y=y;}
    bool friend operator <(Vector n1,Vector n2){return cmp(n1.x,n2.x)?n1.y<n2.y:n1.x<n2.x;}
    Vector friend operator -(Vector n1,Vector n2){return Vector(n1.x-n2.x,n1.y-n2.y);}
}pot[N],s[N];
int n,tot;
double Cross(Point n1,Point n2){return n1.x*n2.y-n1.y*n2.x;}
double Dis(Point n1,Point n2){return sqrt((n1.x-n2.x)*(n1.x-n2.x)+(n1.y-n2.y)*(n1.y-n2.y));}
void push(Point n)
{
    while(tot>1&&Cross(s[tot]-s[tot-1],n-s[tot])<0) --tot;
    s[++tot]=n;
}
int main()
{
    scanf("%d",&n);
    for(int i=1;i<=n;i++) scanf("%lf%lf",&pot[i].x,&pot[i].y);
    std::sort(pot+1,pot+1+n);
    s[++tot]=pot[1];
    for(int i=2;i<=n;i++) push(pot[i]);
    for(int i=n-1;i;i--) push(pot[i]);
    double ans=Dis(s[1],s[tot]);
    for(int i=2;i<=tot;i++) ans+=Dis(s[i],s[i-1]);
    printf("%.2lf
",ans);
    return 0;
}

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2018.12.27