ZOJ1453

求一个凸包= =...直接上模板

#include<bits/stdc++.h>using namespace std;int n;void Gao(){    vector<VEC> a,b;    for (int i=0;i<n;i++)    {        VEC tem;        cin>>tem.x>>tem.y;        a.push_back(tem);    }    b=convex_hull(a);    double ans=0.0;    for (int i=0;i<b.size();i++)    {        int j=i+1;        if (j==b.size())            j=0;        VEC tem=b[i]-b[j];        double xx=tem.x,yy=tem.y;        ans+=sqrt(xx*xx+yy*yy);    }    printf("%.2lf\n",ans);}int main(){    //freopen("a.in","r",stdin);    while (cin>>n &&n)        Gao();    return 0;}