POJ 3130

这题，加了精度错了，不加精度反而对了。。。

#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
#include <cmath>
using namespace std;
const int MAXN=110;
const double eps=1e-8;

struct point {
    double x,y;
};
point pts[MAXN],p[MAXN],q[MAXN];
int n,cCnt,curCnt;

int DB(double d){
    if(d>eps) return 1;
    if(d<-eps) return -1;
    return 0;
}

void initial(){
    for(int i=1;i<=n;i++)
    p[i]=pts[i];
    p[n+1]=p[1];
    p[0]=p[n];
    cCnt=n;
}

void getline(point x,point y,double &a,double &b,double &c){
    a = y.y - x.y;
    b = x.x - y.x;
    c = y.x * x.y - x.x * y.y;
}

point intersect(point x,point y,double a,double b,double c){
    double u = fabs(a * x.x + b * x.y + c);
    double v = fabs(a * y.x + b * y.y + c);
    point pt;
    pt.x=(x.x * v + y.x * u) / (u + v);
    pt.y=(x.y * v + y.y * u) / (u + v);
    return  pt;
}

void cut(double a,double b,double c){
    curCnt=0;
    for(int i=1;i<=cCnt;i++){
        if(a*p[i].x+b*p[i].y+c <=0) q[++curCnt] = p[i];
        else {
            if(a*p[i-1].x + b*p[i-1].y + c <=0){
                q[++curCnt] = intersect(p[i],p[i-1],a,b,c);
            }
             if(a*p[i+1].x + b*p[i+1].y + c <=0){
                q[++curCnt] = intersect(p[i],p[i+1],a,b,c);
            }
        }
    }
    for(int i = 1; i <= curCnt; ++i)p[i] = q[i];
    p[curCnt+1] = q[1];p[0] = p[curCnt];
    cCnt = curCnt;
}

void slove(){
    initial();
    for(int i=1;i<=n;i++){
        double a,b,c;
        getline(pts[i],pts[i+1],a,b,c);
        cut(a,b,c);
    }
}

int main(){
    while(true){
        scanf("%d",&n);
        if(n==0) break;
        for(int i=1;i<=n;i++)
        scanf("%lf%lf",&pts[i].x,&pts[i].y);
        pts[n+1]=pts[1];
        slove();
        if(cCnt>=1) printf("1\n");
        else printf("0\n");
    }
    return 0;
}

POJ 3130