ZOJ 1453 Surround the Trees(凸包入门:求凸包周长)

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http://acm.zju.edu.cn/onlinejudge/showProblem.do?problemCode=1453

题意:

平面上有n个点,要你求出这n个点的凸包的周长.

分析:

直接用刘汝佳的模板求出凸包即可,在ch[i]数组中按顺序保存了所有的凸包点,然后循环一边计算周长即可.

AC代码:

#include<cstdio>#include<cstring>#include<algorithm>#include<cmath>using namespace std;const double eps=1e-10;int dcmp(double x){    if(fabs(x)<eps) return 0;    return x<0?-1:1;}struct Point{    double x,y;    Point(){}    Point(double x,double y):x(x),y(y){}    bool operator==(const Point& B)const    {        return dcmp(x-B.x)==0 && dcmp(y-B.y)==0;    }    bool operator<(const Point& B)const    {        return dcmp(x-B.x)<0 || (dcmp(x-B.x)==0 && dcmp(y-B.y)<0 );    }};typedef Point Vector;Vector operator-(Point A,Point B){    return Vector(A.x-B.x,A.y-B.y);}double Cross(Vector A,Vector B)//叉积{    return A.x*B.y-A.y*B.x;}int ConvexHull(Point *p,int n,Point *ch)//凸包{    sort(p,p+n);    n=unique(p,p+n)-p;    int m=0;    for(int i=0;i<n;i++)    {        while(m>1 && Cross(ch[m-1]-ch[m-2], p[i]-ch[m-2])<=0) m--;        ch[m++]=p[i];    }    int k=m;    for(int i=n-2;i>=0;i--)    {        while(m>k && Cross(ch[m-1]-ch[m-2], p[i]-ch[m-2])<=0) m--;        ch[m++]=p[i];    }    if(n>1) m--;    return m;}/***以上是刘汝佳模板***/const int maxn=100+5;Point p[maxn],ch[maxn];int main(){    int n;    while(scanf("%d",&n)==1 && n)    {        for(int i=0;i<n;i++)            scanf("%lf%lf",&p[i].x,&p[i].y);        int m=ConvexHull(p,n,ch);        double ans=0;//总周长        ch[m]=ch[0];        for(int i=0;i<m;i++)            ans+= sqrt((ch[i].x-ch[i+1].x)*(ch[i].x-ch[i+1].x)+(ch[i].y-ch[i+1].y)*(ch[i].y-ch[i+1].y));        printf("%.2lf\n",ans);    }    return 0;}

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