bzoj1074

题意:

给你n次折叠

m个询问

每次询问折叠后，xi,yi有几层

题解：

计算几何

模拟

#include<cstdio>  
#include<cstdlib>  
#include<cmath>  
using namespace std;  
int n,m;  
double px[15],py[15],qx[15],qy[15];  
int dcmp(double a,double b)
{  
    if (fabs(a-b)<=1e-9) return 0;  
    if (a<b)return -1;  
    return 1;  
}  
double Cross(double x1,double y1,double x2,double y2)
{  
    return x1*y2-x2*y1;  
}    
void calc(double x1,double y1,double x0,double y0,double &retx,double &rety)
{  
    retx=(x0*(x1*x0+y1*y0)+y0*(x0*y1-x1*y0))/(x0*x0+y0*y0);  
    rety=(y0*(x1*x0+y1*y0)-x0*(x0*y1-x1*y0))/(x0*x0+y0*y0);  
}    
int dp(double x,double y,int t)  
{  
    if (!t)  
     {  
        if (dcmp(x,100.0)<0&&dcmp(x,0.0)>0&&dcmp(y,100.0)<0&&dcmp(y,0.0)>0)
         return 1;  
        return 0;  
     }  
    if (dcmp(Cross(x-px[t],y-py[t],qx[t]-px[t],qy[t]-py[t]),0.0)>=0)return 0;  
    else  
     {  
        double retx,rety;  
        calc(x-px[t],y-py[t],qx[t]-px[t],qy[t]-py[t],retx,rety);  
        retx+=px[t];rety+=py[t];  
        return dp(x,y,t-1)+dp(retx,rety,t-1);  
     }  
}  
int main()  
{  
    double _x,_y;  
    scanf("%d",&n);  
    for (int i=1;i<=n;i++)scanf("%lf%lf%lf%lf",&px[i],&py[i],&qx[i],&qy[i]);  
    scanf("%d",&m);  
    while (m--)  
     {  
        scanf("%lf%lf",&_x,&_y);  
        printf("%d
",dp(_x,_y,n));  
     }  
    return 0;  
}