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  • 二维凸包的板子

    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;
    }
    

    2018.12.27

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  • 原文地址:https://www.cnblogs.com/butterflydew/p/10185369.html
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