题解：计算凸包周长
#include <iostream>
#include <cmath>
#include <algorithm>
const int size=1000;
using namespace std;
struct pint{int x,y;}x[size];
int n,l,ans[size],cnt,sta[size],tail;
bool cmp(pint a,pint b){return (a.y1 && !crossleft(x[sta[tail-1]],x[sta[tail-2]],x[i]))
tail--;
sta[tail++]=i;
}
for(int i=0;i<tail;i++)
ans[cnt++]=sta[i];
tail=0;
sta[tail++]=n-1;
sta[tail++]=n-2;
for(int i=n-3 ;i>=0;i--){
while(tail>1 && !crossleft(x[sta[tail-1]],x[sta[tail-2]],x[i]))
tail--;
sta[tail++]=i;
}
for(int i=0;i<tail;i++)
ans[cnt++]=sta[i];
}
int main(){
int tt;
while(scanf("%d",&tt)!=EOF){
while(tt--){
scanf("%d%d",&n,&l);
for(int i=0;i<n;i++)
scanf("%d%d",&x[i].x,&x[i].y);
jarvis();
double re=4*acos(0.0)*l;
for(int i=0;i<cnt-1;i++)
re+=sqrt((x[ans[i]].x-x[ans[i+1]].x)*(x[ans[i]].x-x[ans[i+1]].x)*1.0
+(x[ans[i]].y-x[ans[i+1]].y)*(x[ans[i]].y-x[ans[i+1]].y)*1.0);
printf("%.0lf
",re);
if(tt)
printf("
");
}
}
return 0;
}