HDU 1348 Wall

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\n",re);
                if(tt)
                printf("\n");
        }
    }
    return 0;
}