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[],py[],qx[],qy[];
int dcmp(double a,double b)
{
    if (fabs(a-b)<=1e-) return ;
    if (a<b)return -;
    return ;
}
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)<&&dcmp(x,0.0)>&&dcmp(y,100.0)<&&dcmp(y,0.0)>)
         return ;
        return ;
     }
    if (dcmp(Cross(x-px[t],y-py[t],qx[t]-px[t],qy[t]-py[t]),0.0)>=)return ;
    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-)+dp(retx,rety,t-);
     }
}
int main()
{
    double _x,_y;
    scanf("%d",&n);
    for (int i=;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\n",dp(_x,_y,n));
     }
    return ;
}