codeforces #339 div 2 C. Peter and Snow Blower

 1#include <cstdio>
 2#include <cstring>
 3#include <iostream>
 4#include <algorithm>
 5#include <vector>
 6#include <queue>
 7#include <set>
 8#include <map>
 9#include <string>
10#include <cmath>
11#include <cstdlib>
12#include <ctime>
13#define fst first
14#define sec second
15#define lson l,m,rt<<1
16#define rson m+1,r,rt<<1|1
17#define ms(a,x) memset(a,x,sizeof(a))
18typedef long long LL;
19#define pi pair < int ,int >
20#define MP make_pair

1using namespace std;
2const double eps = 1E-8;
3const int dx4[4]={1,0,0,-1};
4const int dy4[4]={0,-1,1,0};
5const int inf = 0x3f3f3f3f;
6const int N = 1E5+7;
7const double PI = acos(-1.0);

 1int dblcmp(double d)
 2{
 3    return d<-eps?-1:d>eps;
 4}
 5struct point
 6{
 7    double x,y;
 8    point (){}
 9    point (double _x,double _y):
10	x(_x),y(_y){};
11    void input()
12    {
13	cin>>x>>y;
14    }
15    point sub(point p)
16    {
17	return point (x-p.x,y-p.y);
18    }
19    double dot(point p)
20    {
21	return x*p.x+y*p.y;
22    }
23    double distance2(point p)
24    {
25	return (x-p.x)*(x-p.x)+(y-p.y)*(y-p.y);
26    }
27    double distance(point p)
28    {
29	return hypot(x-p.x,y-p.y);
30    }
31    double det(point p)
32    {
33	return x*p.y-y*p.x;
34    }
35}p[N],q;
36double sqr(double x)
37{
38    return x*x;
39}
40struct line
41{
42    point a,b;
43    line(){}
44    line (point _a,point _b)
45    {
46	a = _a;
47	b = _b;
48    }
49    double length()
50    {
51	return a.distance(b);
52    }

 1    double dispointtoline2(point p)
 2    {
 3	double res = sqr(fabs(p.sub(a).det(b.sub(a)))/length());
 4//	cout<<"res:"<<res<<endl;
 5	return res;
 6    }
 7    double dispointtoseg2(point p)
 8    {
 9	if (dblcmp(p.sub(b).dot(a.sub(b)))<0||dblcmp(p.sub(a).dot(b.sub(a)))<0)
10	    return min(p.distance2(a),p.distance2(b));

1    return dispointtoline2(p);
2    }
3}li[N];

1int n;
2int main()
3{
4	#ifndef  ONLINE_JUDGE 
5	freopen("code/in.txt","r",stdin);
6  #endif

 1	cin>>n;
 2	q.input();
 3	double MIN = 99999999999999999;
 4	double MAX = -1;
 5	for ( int i = 1 ; i <= n ; i++)
 6	{
 7	    p[i].input();
 8	    double d= p[i].distance2(q);
 9	    MAX = max(MAX,d);
10	}

 1	for ( int i = 1 ; i <= n-1 ; i++)
 2	{
 3	    li[i] = line(p[i],p[i+1]);
 4	}
 5	li[n]=line(p[n],p[1]);
 6	for ( int i = 1 ; i <= n ; i++)
 7	{
 8	    double d = li[i].dispointtoseg2(q);
 9//	    cout<<li[i].a.x<<" "<<li[i].a.y<<"   "<<li[i].b.x<<" "<<li[i].b.y<<endl; 
10	//    cout<<"d:"<<d<<endl;
11	    MIN = min(MIN,d);
12	}
13//	cout<<"MAX:"<<MAX<<"  MIN:"<<MIN<<endl;
14	double ans = (MAX-MIN)*PI;
15	printf("%.18f\n",ans);

1  #ifndef ONLINE_JUDGE  
2  fclose(stdin);
3  #endif
4    return 0;
5}