UVa 378 - Intersecting Lines

 1 #include <iostream>
 2 #include <cstdio>
 3 #include <cstring>
 4 #include <cstdlib>
 5 using namespace std;
 6 struct point{
 7     int x,y;
 8     point(int x = 0,int y = 0){
 9         this->x = x;
10         this->y = y;
11     }
12 };
13 struct line{
14     point st,en;
15     line(){}
16 };
17 class Intersect {
18     private:
19         line la,lb;
20     public:
21         void readData();
22         void process();
23         bool isCross();//
24         bool isSameLine();
25 };
26 void Intersect::readData(){
27     point p1,p2,p3,p4;
28     cin>>p1.x>>p1.y>>p2.x>>p2.y>>p3.x>>p3.y>>p4.x>>p4.y;
29     la.st = p1;la.en = p2;
30     lb.st = p3;lb.en = p4;
31 }
32 void Intersect::process(){
33     if(isCross()){
34         //求出交点
35         double A1 = la.st.y - la.en.y,B1 = la.en.x - la.st.x;
36         double C1 = la.st.x * la.en.y - la.st.y * la.en.x;//A1,B1,C1是方程系数
37         double A2 = lb.st.y - lb.en.y,B2 = lb.en.x - lb.st.x;
38         double C2 = lb.st.x * lb.en.y - lb.st.y * lb.en.x;
39         double x = (B1*C2 - B2*C1)/(A1*B2 - A2*B1);
40         double y = (C1*A2 - C2*A1)/(A1*B2 - A2*B1);//方程的解
41         printf("POINT %.2lf %.2lf\n",x,y);
42     }
43     else{
44         if(isSameLine()==0){
45             cout<<"LINE"<<endl;
46         }
47         else
48             cout<<"NONE"<<endl;
49     }
50 }
51 bool Intersect::isCross(){//判断是否是相交的
52     if((la.en.x - la.st.x)*(lb.en.y - lb.st.y) ==
53        (la.en.y - la.st.y)*(lb.en.x - lb.st.x)){
54        return false;
55     }
56     else
57         return true;
58 }
59 bool Intersect::isSameLine(){//用向量叉积判断点是否在线上
60     return (lb.st.x-lb.en.x)*(la.st.y-lb.en.y)-(la.st.x-lb.en.x)*(lb.st.y-lb.en.y);
61 }
62 int main()
63 {
64     int cases;
65     Intersect intersect;
66     #ifndef ONLINE_JUDGE
67         freopen("D://acm.txt","r",stdin);
68     #endif // ONLINE_JUDGE
69     while(cin>>cases){
70         cout<<"INTERSECTING LINES OUTPUT"<<endl;
71         while(cases--){
72             intersect.readData();
73             intersect.process();
74         }
75         cout<<"END OF OUTPUT"<<endl;
76     }
77     return 0;
78 }