lightoj 1260

两个多边形，问在职中穿行的圆的最大半径。

裸的点到线段距离，当模板了。

#include <cstdio>
#include <cstring>
#include <vector>
#include <cmath>
#include <stack>
#include <cstdlib>
#include <queue>
#include <map>
#include <iostream>
#include <algorithm>
#include <bits/stdc++.h>
#include <queue>
#include <ctime>

using namespace std;
struct Point
{
    double x,y;
}pa[110],pb[110];
double GetPointDistance(Point p1, Point p2)
{
    return sqrt((p1.x-p2.x)*(p1.x-p2.x)+(p1.y-p2.y)*(p1.y-p2.y));
}
double GetNearestDistance(Point PA, Point PB, Point P3)
{
    double a,b,c;
    a=GetPointDistance(PB,P3);
    if(a<=0.00001)
        return 0.0f;
    b=GetPointDistance(PA,P3);
    if(b<=0.00001)
        return 0.0f;
    c=GetPointDistance(PA,PB);
    if(c<=0.00001)
        return a;//如果PA和PB坐标相同，则退出函数，并返回距离

    if(a*a>=b*b+c*c)//--------图3--------
        return b;      //如果是钝角返回b
    if(b*b>=a*a+c*c)//--------图4-------
        return a;      //如果是钝角返回a
    
    double s=abs((PB.x-PA.x)*(P3.y-PA.y)-(P3.x-PA.x)*(PB.y-PA.y))/2.0;
    return 2*s/c;
}
int main()
{
    int T,ncas=1;
    scanf ("%d",&T);
    while (T--)
    {
        memset(pa,0,sizeof(pa));
        memset(pb,0,sizeof(pb));
        int n;
        scanf ("%d",&n);
        for (int i=0;i<n;i++)
        {
            scanf ("%lf%lf",&pa[i].x,&pa[i].y);
        }
        int m;
        scanf ("%d",&m);
        for (int i=0;i<m;i++)
        {
            scanf ("%lf%lf",&pb[i].x,&pb[i].y);
        }
        pb[m]=pb[0];
        double ans=0x7f7f7f7f;
        for (int i=0;i<n;i++)
        {
            for (int j=0;j<m;j++)
            {
                ans=min(ans,GetNearestDistance(pb[j],pb[j+1],pa[i]));
            }
        }
        printf ("Case %d: %.10f\n",ncas++,ans/2.0);
    }
    return 0;
}