求多条线段相交（暴力了点）

#include<stdio.h>#include<math.h>struct point {double x,y;};struct line{point a,b;}g[120];double MAX(double a,double b){return a>b?a:b;}double MIN(double a,double b){return a<b?a:b;}double cross_segment(point a,point b,point c){return (c.x-a.x)*(b.y-a.y)-(b.x-a.x)*(c.y-a.y); }int onsegment(point a,point b,point c){double d1=MIN(a.x,b.x);double d2=MAX(a.x,b.x);double d3=MIN(a.y,b.y);double d4=MAX(a.y,b.y);if(d1<=c.x&&d2>=c.x&&d3<=c.y&&d4>=c.y)return 1;return 0;}int segments(line a,line b){double d1=cross_segment(b.a,b.b,a.a);double d2=cross_segment(b.a,b.b,a.b);double d3=cross_segment(a.a,a.b,b.a);double d4=cross_segment(a.a,a.b,b.b);if(((d1>0&&d2<0)||(d1<0&&d2>0))&&((d3>0&&d4<0)||(d3<0&&d4>0)))return 1;else if(d1==0&&onsegment(b.a,b.b,a.a))return 1;else if(d2==0&&onsegment(b.a,b.b,a.b))return 1;else if(d3==0&&onsegment(a.a,a.b,b.a))return 1;else if(d4==0&&onsegment(a.a,a.b,b.b))return 1;elsereturn 0;}int main(){int i,j,k,m,n,ncase,sum;while(scanf("%d",&m),m){for(i=0;i<m;i++)scanf("%lf%lf%lf%lf",&g[i].a.x,&g[i].a.y,&g[i].b.x,&g[i].b.y);sum=0;if(m==1){printf("0\n");continue;}for(i=0;i<m;i++){for(j=i+1;j<m;j++){if(segments(g[i],g[j]))sum++;}}printf("%d\n",sum);}return 0;}