判断两线段相交

 

 

 

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#include <iostream> #include <cstdio> #include <algorithm> #include <string.h> #include <stdlib.h> using namespace std; int n; struct point {     double x;     double y; }; struct v {     point s;     point e; } q[102]; int sum; double multi(struct point p1,struct point p2,struct point p0) {     return (p1.x-p0.x)*(p2.y-p0.y)-(p2.x-p0.x)*(p1.y-p0.y); } int main() {     while(scanf("%d",&n)!=EOF&&n!=0)     {         sum=0;         for(int i=0; i<n; i++)         {             scanf("%lf%lf%lf%lf",&q[i].s.x,&q[i].s.y,&q[i].e.x,&q[i].e.y);         }         for(int i=0; i<n; i++)         {             for(int j=i+1; j<n; j++)             {                 if(max(q[i].s.x,q[i].e.x)>=min(q[j].s.x,q[j].e.x)&&                         min(q[i].s.x,q[i].e.x)<=max(q[j].s.x,q[j].e.x)&&                         max(q[i].s.y,q[i].e.y)>=min(q[j].s.y,q[j].e.y)&&                         min(q[i].s.y,q[i].e.y)<=max(q[j].s.y,q[j].e.y)&&                         multi(q[j].s,q[i].e,q[i].s)*multi(q[i].e,q[j].e,q[i].s)>=0&&                         multi(q[i].s,q[j].e,q[j].s)*multi(q[j].e,q[i].e,q[j].s)>=0)                     sum++;             }         }         cout<<sum<<endl;     }     return 0; }