Codeforces Gym 100338B Geometry Problem 计算几何

Problem B. Geometry Problem
Time Limit: 20 Sec

Memory Limit: 256 MB

题目连接

http://acm.hust.edu.cn/vjudge/contest/view.action?cid=88926#problem/B

Description

Peter is studying in the third grade of elementary school. His teacher of geometry often gives him difficult home tasks. At the last lesson the students were studying circles. They learned how to draw circles with compasses. Peter has completed most of his homework and now he needs to solve the following problem. He is given two segments. He needs to draw a circle which intersects interior of each segment exactly once. The circle must intersect the interior of each segment, just touching or passing through the end of the segment is not satisfactory. Help Peter to complete his homework.

Input

The input file contains several test cases. Each test case consists of two lines. The first line of the test case contains four integer numbers x11, y11, x12, y12 — the coordinates of the ends of the first segment. The second line contains x21, y21, x22, y22 and describes the second segment in the same way. Input is followed by two lines each of which contains four zeroes these lines must not be processed. All coordinates do not exceed 102 by absolute value.

Output

For each test case output three real numbers — the coordinates of the center and the radius of the circle. All numbers in the output file must not exceed 1010 by their absolute values. The jury makes all comparisons of real numbers with the precision of 10−4 .

Sample Input

0 0 0 4
1 0 1 4
0 0 0 0
0 0 0 0

Sample Output

0.5 0 2

HINT

题意

给你两个线段，让你构造一个圆，与每个线段都只相交一次

题解：

首先如何判断这个线段和圆相交了一次：一个端点在圆内，一个在圆外

然后我们枚举四个点的中点，半径就取中点到端点的最小值，然后再随便加上一个0.005就好了

就AC了……

加0.05会WA8

代码：

//qscqesze
#include <cstdio>
#include <cmath>
#include <cstring>
#include <ctime>
#include <iostream>
#include <algorithm>
#include <set>
#include <vector>
#include <sstream>
#include <queue>
#include <typeinfo>
#include <fstream>
#include <map>
#include <stack>
typedef long long ll;
using namespace std;
//freopen("D.in","r",stdin);
//freopen("D.out","w",stdout);
#define sspeed ios_base::sync_with_stdio(0);cin.tie(0)
#define maxn 200051
#define mod 10007
#define eps 1e-9
int Num;
//const int inf=0x7fffffff;   //нчоч╢С
const int inf=0x3f3f3f3f;
inline ll read()
{
    ll x=0,f=1;char ch=getchar();
    while(ch<'0'||ch>'9'){if(ch=='-')f=-1;ch=getchar();}
    while(ch>='0'&&ch<='9'){x=x*10+ch-'0';ch=getchar();}
    return x*f;
}
//**************************************************************************************

struct node
{
    double x,y;
};
node kiss1[4];
node kiss2[4];
double dis(node a,node b)
{
    return sqrt((a.x-b.x)*(a.x-b.x)+(a.y-b.y)*(a.y-b.y));
}
int check1(double r,double x,double y)
{
    int flag=0;
    int flag1=0;
    node ttt;
    ttt.x=x,ttt.y=y;
    for(int i=0;i<2;i++)
    {
        if(dis(ttt,kiss1[i])<r)
            flag++;
        if(dis(ttt,kiss2[i])<r)
            flag1++;
    }
    if(flag==1&&flag1==1)
        return 1;
    return 0;
}
int check(double x,double y)
{
    double ans=inf;
    node a;
    a.x=x,a.y=y;
    for(int i=0;i<2;i++)
    {
        ans = min(ans,dis(a,kiss1[i]));
        ans = min(ans,dis(a,kiss2[i]));
    }
    ans+=0.005;
    if(check1(ans,x,y))
    {
        printf("%.10f %.10f %.10f
",x,y,ans);
        return 1;
    }
    return 0;
}
int main()
{ 
    srand((unsigned)time(NULL));
    freopen("geometry.in","r",stdin);
    freopen("geometry.out","w",stdout);
    while(1)
    {
        for(int i=0;i<2;i++)
            cin>>kiss1[i].x>>kiss1[i].y;
        for(int i=0;i<2;i++)
            cin>>kiss2[i].x>>kiss2[i].y;
        if(kiss1[0].x==0&&kiss1[0].y==0&&kiss2[0].x==0&&kiss2[0].y==0&&kiss1[1].x==0&&kiss1[1].y==0&&kiss2[1].x==0&&kiss2[1].y==0)
            break;
        node a,b;
        double ans=inf;
        int flag = 1;
        for(int i=0;i<2;i++)
        {
            for(int j=0;j<2;j++)
            {
                a = kiss1[i],b = kiss2[j];
                double ansx=(a.x+b.x)/2.0;
                double ansy=(a.y+b.y)/2.0;
                if(check(ansx,ansy)==1)
                {
                    flag = 0;
                    break;
                }
            }
            if(!flag)
                break;
        }
        if(!flag)
            continue;
    }
}