PKU1039

几何题

#include<math.h>
#include<string.h>
#include <stdio.h>


struct Point
{
    double x,y;
};

struct Line
{
    double x1, y1;
    double x2, y2;
};
int n;
double x[20],y[20];
Line line;
int result;
double dis;


Point cut(Line l)
{
    double a1, b1, a2, b2;
    a1=(line.y2-line.y1)/(line.x2-line.x1);
    b1=line.y1-a1*line.x1;
    a2=(l.y2-l.y1)/(l.x2-l.x1);
    b2=l.y1-a1*l.x1;
    Point p;
    p.x=(b2-b1)/(a1-a2);
    p.y=a1*p.x+b1;
    return p;
}


double ppdis(Point p1, Point p2)
{
    return sqrt((p1.x-p2.x)*(p1.x-p2.x)+(p1.y-p2.y)*(p1.y-p2.y));
}


double distance()
{
    double dis1, dis2;
    Point p1,p2,p3;
    p1.x=0, p1.y=(line.y2-line.y1)/(line.x2-line.x1)*(0-line.x1)+line.y1;

    Line line1, line2;

    line1.x1=x[result-1];
    line1.y1=y[result-1];
    line1.x2=x[result];
    line1.y2=y[result];
    p2=cut(line1);

    line2.x1=x[result-1];
    line2.y1=y[result-1]-1;
    line2.x2=x[result];
    line2.y2=y[result]-1;
    p3=cut(line2);

    dis1=ppdis(p1,p2);
    dis2=ppdis(p1,p3);
//    printf("%d  %lf   %lf\n",result, p2.x,p2.y);
    if(dis1 < dis2)
        return dis2;
    else
        return dis1;

}


bool thro(int i)
{
    double holdy=(line.y2-line.y1)/(line.x2-line.x1)*(x[i]-line.x1)+line.y1;
    if(holdy >= y[i] - 1  &&  holdy <= y[i])
        return 1;
    else
        return 0;
}


int cnt()
{
    int i;
    for(i = 0; i < n; i++)
    {
        if(!thro(i))
            break;
    }
    return i;
}


void func()
{
    int i, j;
    int res;
    for(i = 0; i < n; i++)
    {
        for(j = i+1; j < n; j++)
        {
            line.x1=x[i];
            line.y1=y[i];
            line.x2=x[j];
            line.y2=y[j];
            res=cnt();
            if(result<res)
            {
                result=res;
                dis=distance();
            }

            line.x1=x[i];
            line.y1=y[i];
            line.x2=x[j];
            line.y2=y[j]-1;
            res=cnt();
            if(result<res)
            {
                result=res;
                dis=distance();
            }

            line.x1=x[i];
            line.y1=y[i]-1;
            line.x2=x[j];
            line.y2=y[j];
            res=cnt();
            if(result<res)
            {
                result=res;
                dis=distance();
            }

            line.x1=x[i];
            line.y1=y[i]-1;
            line.x2=x[j];
            line.y2=y[j]-1;
            res=cnt();
            if(result<res)
            {
                result=res;
                dis=distance();
            }
        }
    }

}


int main()
{    
    while(scanf("%d", &n)!=EOF)
    {
        if(n == 0)
            break;
        result=0;
        dis=0;
        int i;        
        for(i = 0; i < n; i++)
        {
            scanf("%lf%lf", &x[i], &y[i]);
        }
        func();
/**//*        line.x1=0,line.y1=1,line.x2=4,line.y2=1;
        int xx=thro(3);
        printf("%d\n",xx);*/
        if(result < n)
            printf("%.2f\n",dis);
        else
            printf("Through all the pipe.\n");
    }
    return 0;
}