first i find the convex polygon
the answer is equal to the length of the convex polygon and 2*pi*l

is it right?


#include <stdio.h>
#include <math.h>

#define PI 3.1415926535

struct point
{
double x,y;
};

struct point p[1001];
int n;
double l;
double dis;

double mul(point p1,point p2,point p0)
{
return ((p1.x-p0.x)*(p2.y-p0.y)-(p2.x-p0.y)*(p1.y-p0.y));
}

double dist(point q,point p)
{
return (sqrt((p.x-q.x)*(p.x-q.x)+(p.y-q.y)*(p.y-q.y)));
}

void init()
{
int i,j;
//FILE *fp=fopen("input.in","r");
scanf("%d%lf",&n,&l);
for (i=0;i<n;i++)
 scanf("%lf%lf",&p[i].x,&p[i].y);
}


void work()
{
int i,j;
int s;
int next[1001];
for (i=0;i<n;i++)
 next[i]=(i+1)%n;
s=1;
while (s==1)
 {
 s=0;
 for (i=0;i<n;i++)
  if (next[i]!=-1)
   {
   if (mul(p[next[i]],p[next[next[i]]],p[i])>=-1e-14)
    {
    s=1;
    j=next[i];
    next[i]=next[next[i]];
    next[j]=-1;
    }
   }
  }
dis=0;
for (i=0;i<n;i++)
 if (next[i]!=-1)
  dis=dis+dist(p[i],p[next[i]]);
dis=dis+2*PI*l;
printf("%.0lf\n",dis+0.5);
}

main()
{
init();
work();
return 0;
}

> first i find the convex polygon
> the answer is equal to the length of the convex polygon and 2*pi*l
>
> is it right?
>
>
> #include <stdio.h>
> #include <math.h>
>
> #define PI 3.1415926535
>
> struct point
> {
> double x,y;
> };
>
> struct point p[1001];
> int n;
> double l;
> double dis;
>
> double mul(point p1,point p2,point p0)
> {
> return ((p1.x-p0.x)*(p2.y-p0.y)-(p2.x-p0.y)*(p1.y-p0.y));
> }
>
> double dist(point q,point p)
> {
> return (sqrt((p.x-q.x)*(p.x-q.x)+(p.y-q.y)*(p.y-q.y)));
> }
>
> void init()
> {
> int i,j;
> //FILE *fp=fopen("input.in","r");
> scanf("%d%lf",&n,&l);
> for (i=0;i<n;i++)
>  scanf("%lf%lf",&p[i].x,&p[i].y);
> }
>
>
> void work()
> {
> int i,j;
> int s;
> int next[1001];
> for (i=0;i<n;i++)
>  next[i]=(i+1)%n;
> s=1;
> while (s==1)
>  {
>  s=0;
>  for (i=0;i<n;i++)
>   if (next[i]!=-1)
>    {
>    if (mul(p[next[i]],p[next[next[i]]],p[i])>=-1e-14)
>     {
>     s=1;
>     j=next[i];
>     next[i]=next[next[i]];
>     next[j]=-1;
>     }
>    }
>   }
> dis=0;
> for (i=0;i<n;i++)
>  if (next[i]!=-1)
>   dis=dis+dist(p[i],p[next[i]]);
> dis=dis+2*PI*l;
> printf("%.0lf\n",dis+0.5);
> }
>
> main()
> {
> init();
> work();
> return 0;
> }

> > first i find the convex polygon
> > the answer is equal to the length of the convex polygon and 2*pi*l
> >
> > is it right?
> >
> >
> > #include <stdio.h>
> > #include <math.h>
> >
> > #define PI 3.1415926535
> >
> > struct point
> > {
> > double x,y;
> > };
> >
> > struct point p[1001];
> > int n;
> > double l;
> > double dis;
> >
> > double mul(point p1,point p2,point p0)
> > {
> > return ((p1.x-p0.x)*(p2.y-p0.y)-(p2.x-p0.y)*(p1.y-p0.y));
> > }
> >
> > double dist(point q,point p)
> > {
> > return (sqrt((p.x-q.x)*(p.x-q.x)+(p.y-q.y)*(p.y-q.y)));
> > }
> >
> > void init()
> > {
> > int i,j;
> > //FILE *fp=fopen("input.in","r");
> > scanf("%d%lf",&n,&l);
> > for (i=0;i<n;i++)
> >  scanf("%lf%lf",&p[i].x,&p[i].y);
> > }
> >
> >
> > void work()
> > {
> > int i,j;
> > int s;
> > int next[1001];
> > for (i=0;i<n;i++)
> >  next[i]=(i+1)%n;
> > s=1;
> > while (s==1)
> >  {
> >  s=0;
> >  for (i=0;i<n;i++)
> >   if (next[i]!=-1)
> >    {
> >    if (mul(p[next[i]],p[next[next[i]]],p[i])>=-1e-14)
> >     {
> >     s=1;
> >     j=next[i];
> >     next[i]=next[next[i]];
> >     next[j]=-1;
> >     }
> >    }
> >   }
> > dis=0;
> > for (i=0;i<n;i++)
> >  if (next[i]!=-1)
> >   dis=dis+dist(p[i],p[next[i]]);
> > dis=dis+2*PI*l;
> > printf("%.0lf\n",dis+0.5);
> > }
> >
> > main()
> > {
> > init();
> > work();
> > return 0;
> > }