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