poj 3384 Feng Shui

#include <cmath>
#include <cstdio>
#include <cstdlib>
#include <iostream>
#include <cstring>
#include <string>
#include <algorithm>
#include <queue>
#include <stack>
#include <climits>

using namespace std;

const int MAX = 110;
struct point {double x,y;};
struct line{point a,b; double ang;};
point p[MAX],s[MAX];
line ln[MAX],deq[MAX];
const double eps = 1e-6;
bool dy(double x,double y)	{	return x > y + eps;}	// x > y 
bool xy(double x,double y)	{	return x < y - eps;}	// x < y 
bool dyd(double x,double y)	{ 	return x > y - eps;}	// x >= y 
bool xyd(double x,double y)	{	return x < y + eps;} 	// x <= y 
bool dd(double x,double y) 	{	return fabs( x - y ) < eps;}  // x == y
double disp2p(point a,point b) //  a b         
{
	return sqrt( ( a.x - b.x ) * ( a.x - b.x ) + ( a.y - b.y ) * ( a.y - b.y ) );
}
double crossProduct(point a,point b,point c)//   ac   ab     
{
	return (c.x - a.x)*(b.y - a.y) - (b.x - a.x)*(c.y - a.y);
}
bool parallel(line u,line v)
{
	return dd( (u.a.x - u.b.x)*(v.a.y - v.b.y) - (v.a.x - v.b.x)*(u.a.y - u.b.y) , 0.0 );
}
point l2l_inst_p(line l1,line l2)
{
	point ans = l1.a;
	double t = ((l1.a.x - l2.a.x)*(l2.a.y - l2.b.y) - (l1.a.y - l2.a.y)*(l2.a.x - l2.b.x))/
			   ((l1.a.x - l1.b.x)*(l2.a.y - l2.b.y) - (l1.a.y - l1.b.y)*(l2.a.x - l2.b.x));
	ans.x += (l1.b.x - l1.a.x)*t;
	ans.y += (l1.b.y - l1.a.y)*t;
	return ans;
}

bool equal_ang(line a,line b)	//    unique      
{
	return dd(a.ang,b.ang);
}
bool cmphp(line a,line b)	//         
{
	if( dd(a.ang,b.ang) ) return xy(crossProduct(b.a,b.b,a.a),0.0);
	return xy(a.ang,b.ang);
}
bool equal_p(point a,point b)//   unique      
{
	return dd(a.x,b.x) && dd(a.y,b.y);
}
void makeline_hp(double x1,double y1,double x2,double y2,line &l)
{
	l.a.x = x1; l.a.y = y1; l.b.x = x2; l.b.y = y2;
	l.ang = atan2(y2 - y1,x2 - x1);
}
void makeline_hp(point a,point b,line &l) //   (  ab)        
{
	l.a = a; l.b = b;
	l.ang = atan2(b.y - a.y,b.x - a.x);	//        ，  a.y - b.y,a.x - b.x 
}
void inst_hp_nlogn(line *ln,int n,point *s,int &len)
{
	len = 0;
	sort(ln,ln+n,cmphp);
	n = unique(ln,ln+n,equal_ang) - ln;
	int bot = 0,top = 1;
	deq[0] = ln[0]; deq[1] = ln[1];
	for(int i=2; i<n; i++)
	{
		if( parallel(deq[top],deq[top-1]) || parallel(deq[bot],deq[bot+1]) )
			return ;
		while( bot < top && dy(crossProduct(ln[i].a,ln[i].b,
			l2l_inst_p(deq[top],deq[top-1])),0.0) )
			top--;
		while( bot < top && dy(crossProduct(ln[i].a,ln[i].b,
			l2l_inst_p(deq[bot],deq[bot+1])),0.0) )
			bot++;
		deq[++top] = ln[i];
	}
	while( bot < top && dy(crossProduct(deq[bot].a,deq[bot].b,
		l2l_inst_p(deq[top],deq[top-1])),0.0) )	top--;
	while( bot < top && dy(crossProduct(deq[top].a,deq[top].b,
		l2l_inst_p(deq[bot],deq[bot+1])),0.0) )	bot++;
	if( top <= bot + 1 ) return ;
	
	for(int i=bot; i<top; i++)
		s[len++] = l2l_inst_p(deq[i],deq[i+1]);
	if( bot < top + 1 ) s[len++] = l2l_inst_p(deq[bot],deq[top]);
	len = unique(s,s+len,equal_p) - s;
} 
void changepoint(point a,point b,point &c,point &d,double h)
{
	double len = disp2p(a,b);
    double dx = h / len * ( a.y - b.y );
	double dy = h / len * (-a.x + b.x );
	c.x = a.x + dx; c.y = a.y + dy;
	d.x = b.x + dx; d.y = b.y + dy;
}
void dis_max(point *p,int len,point &c1,point &c2)
{
	double d = -1e20;
	if( len == 1 )
	{
		c1 = c2 = p[0];
		return ;
	}
	for(int i=0; i<len; i++)
		for(int k=i+1; k<len; k++)
		{
			double l = disp2p(p[i],p[k]);
			if( dy(l,d) )
			{
				d = l;
				c1 = p[i]; c2 = p[k];
			}
		}
}
int main()
{
	int n,len;
	double r;
	point c,d;
	while( ~scanf("%d%lf",&n,&r) )
	{
		for(int i=n-1; i>=0; i--)
			scanf("%lf%lf",&p[i].x,&p[i].y);
		p[n] = p[0];
		for(int i=0; i<n; i++)
		{
			changepoint(p[i],p[i+1],c,d,r);
			makeline_hp(c,d,ln[i]);
		}
		inst_hp_nlogn(ln,n,s,len);
		point c1,c2;
		dis_max(s,len,c1,c2);
		printf("%.4lf %.4lf %.4lf %.4lf
",c1.x,c1.y,c2.x,c2.y);
	}
return 0;
}