POJ 3130 How I Mathematician Wonder What You Are!(半平面交)

和 POJ3335 几乎一模一样。。

//poj3130
#include <stdio.h>
#include <string.h>
#include <iostream>
#include <algorithm>
#include <vector>
#include <queue>
#include <set>
#include <map>
#include <string>
#include <math.h>
#include <stdlib.h>
#include <time.h>
using namespace std;
const double eps = 1e-8;
const double PI = acos(-1.0);
int sgn(double x)
{
if(fabs(x) < eps) return 0;
if(x < 0) return -1;
else return 1;
}
struct Point
{
double x,y;
Point(){}
Point(double _x,double _y)
{
x = _x; y = _y;
}
Point operator -(const Point &b)const
{
return Point(x - b.x, y - b.y);
}
double operator ^(const Point &b)const
{
return x*b.y - y*b.x;
}
double operator *(const Point &b)const
{
return x*b.x + y*b.y;
}
};
struct Line
{
Point s,e;
double k;
Line(){}
Line(Point _s,Point _e)
{
s = _s; e = _e;
k = atan2(e.y - s.y,e.x - s.x);
}
Point operator &(const Line &b)const
{
Point res = s;
double t = ((s - b.s)^(b.s - b.e))/((s - e)^(b.s - b.e));
res.x += (e.x - s.x)*t;
res.y += (e.y - s.y)*t;
return res;
}
};
//半平面交，直线的左边代表有效区域
bool HPIcmp(Line a,Line b)
{
if(fabs(a.k - b.k) > eps)return a.k < b.k;
return ((a.s - b.s)^(b.e - b.s)) < 0;
}
Line Q[110];
void HPI(Line line[], int n, Point res[], int &resn)
{
int tot = n;
sort(line,line+n,HPIcmp);
tot = 1;
for(int i = 1;i < n;i++)
if(fabs(line[i].k - line[i-1].k) > eps)
line[tot++] = line[i];
int head = 0, tail = 1;
Q[0] = line[0];
Q[1] = line[1];
resn = 0;
for(int i = 2; i < tot; i++)
{
if(fabs((Q[tail].e-Q[tail].s)^(Q[tail-1].e-Q[tail-1].s)) < eps || fabs((Q[head].e-Q[head].s)^(Q[head+1].e-Q[head+1].s)) < eps)
return;
while(head < tail && (((Q[tail]&Q[tail-1]) - line[i].s)^(line[i].e-line[i].s)) > eps)
tail--;
while(head < tail && (((Q[head]&Q[head+1]) - line[i].s)^(line[i].e-line[i].s)) > eps)
head++;
Q[++tail] = line[i];
}
while(head < tail && (((Q[tail]&Q[tail-1]) - Q[head].s)^(Q[head].e-Q[head].s)) > eps)
tail--;
while(head < tail && (((Q[head]&Q[head-1]) - Q[tail].s)^(Q[tail].e-Q[tail].e)) > eps)
head++;
if(tail <= head + 1)return;
for(int i = head; i < tail; i++)
res[resn++] = Q[i]&Q[i+1];
if(head < tail - 1)
res[resn++] = Q[head]&Q[tail];
}
Point p[110];
Line line[110];
Point pp[110];
int main()
{
int n;
while(scanf("%d", &n), n)
{
for(int i = 0;i < n;i++) {
scanf("%lf%lf",&p[i].x,&p[i].y);
if (i)
line[i] = Line(p[i-1], p[i]);
}
line[0] = Line(p[n-1], p[0]);
int resn;
HPI(line, n, pp, resn);
puts(resn ? "1" : "0");
}
return 0;
}