Wall--POJ1113(极角排序+求凸包)

#include<stdio.h>
#include<string.h>
#include<stdlib.h>
#include<math.h>
#include<algorithm>
#include<iostream>
#include<queue>

using namespace std;
#define N 1005
#define pi acos(-1.0)
#define ESP 1e-8

int s
;

struct Point
{
double x,y;
Point(double x=0,double y=0):x(x),y(y){}
Point operator - (const Point &temp)const
{
return Point(x-temp.x,y-temp.y);
}
Point operator + (const Point &temp)const
{
return Point(x+temp.x,y+temp.y);
}
bool operator == (const Point &temp)const
{
return (x==temp.x && y==temp.y);
}
double operator * (const Point &temp)const
{
return (x*temp.x+y*temp.y);
}
int operator ^ (const Point &temp)const{
double t=x*temp.y-y*temp.x;
if(t>ESP)
return 1;
if(fabs(t)<ESP)
return 0;
return -1;
}
}a
;

double dist(Point a,Point b)
{
return sqrt((a-b)*(a-b));
}

int cmp(Point a1,Point a2)
{
int t=((a1-a[0])^(a2-a[0]));
if(t==0)
return dist(a1,a[0])<dist(a2,a[0]);
else
return t>0;
}
int top;
void Graham(int n)///求凸包
{
s[0]=0;
s[1]=1;
top=1;
for(int i=2;i<n;i++)
{
while(top>0 && ((a[i]-a[s[top]])^(a[s[top-1]]-a[s[top]]))<=0)
top--;
s[++top]=i;
}

}

int main()
{
int n,l;
while(scanf("%d %d",&n,&l)!=EOF)
{
memset(s,0,sizeof(s));
int k=0;
for(int i=0;i<n;i++)
{
scanf("%lf %lf",&a[i].x,&a[i].y);
if(a[i].y<a[k].y || (a[i].y==a[k].y && a[i].x<a[k].x))
k=i;
}
swap(a[0],a[k]);
sort(a+1,a+n,cmp);

Graham(n);
double C=0;
for(int i=1;i<=top;i++)
{
C+=dist(a[s[i]],a[s[i-1]]);
}
C+=dist(a[s[0]],a[s[top]]);
C+=2*pi*l;
printf("%.0lf\n",C);
}
return 0;
}