http://acm.hdu.edu.cn/showproblem.php?pid=1086
Problem Description
Many geometry(几何)problems were designed in the ACM/ICPC. And now, I also prepare a geometry problem for this final exam. According to the experience of many ACMers, geometry problems are always much trouble, but this problem is very easy, after all we are now attending an exam, not a contest :)
Give you N (1<=N<=100) segments(线段), please output the number of all intersections(交点). You should count repeatedly if M (M>2) segments intersect at the same point.
Note:
You can assume that two segments would not intersect at more than one point.
Give you N (1<=N<=100) segments(线段), please output the number of all intersections(交点). You should count repeatedly if M (M>2) segments intersect at the same point.
Note:
You can assume that two segments would not intersect at more than one point.
Input
Input contains multiple test cases. Each test case contains a integer N (1=N<=100) in a line first, and then N lines follow. Each line describes one segment with four float values x1, y1, x2, y2 which are coordinates of the segment’s ending.
A test case starting with 0 terminates the input and this test case is not to be processed.
A test case starting with 0 terminates the input and this test case is not to be processed.
Output
For each case, print the number of intersections, and one line one case.
Sample Input
2 0.00 0.00 1.00 1.00 0.00 1.00 1.00 0.00 3 0.00 0.00 1.00 1.00 0.00 1.00 1.00 0.000 0.00 0.00 1.00 0.00 0
Sample Output
1 3
求线段相交,交点个数;不过不是很明白为什么不用判平行。
#include<stdio.h>
#include<string.h>
#include<math.h>
#include<iostream>
using namespace std;
struct node
{
double x1,x2,y1,y2;
}g[150];
int cmp(node a,node b)
{
return a.x1<b.x1;
}
int main()
{
int i,j,k,m,n;
double t,tt,ww,xx,yy;
while(scanf("%d",&m)!=EOF)
{
if(m==0)
break;
for(i=0;i<m;i++)
{
scanf("%lf%lf%lf%lf",&g[i].x1,&g[i].y1,&g[i].x2,&g[i].y2);
if(g[i].x1>g[i].x2)
{
t=g[i].x1;
g[i].x1=g[i].x2;
g[i].x2=t;
t=g[i].y1;
g[i].y1=g[i].y2;
g[i].y2=t;
}
}
sort(g,g+m,cmp);
int sum=0;
for(i=0;i<m;i++)
{
for(j=i+1;j<m;j++)
{
if(g[i].x2<g[j].x1)
break;
/*if(((g[i].y2-g[i].y1)*(g[j].x2-g[j].x1)-(g[i].x2-g[i].x1)*(g[j].y2-g[j].y1))<1e-6)
continue;*/
xx=((g[j].y1*g[j].x2-g[j].y2*g[j].x1)*(g[i].x2-g[i].x1)-(g[i].y1*g[i].x2-g[i].y2*g[i].x1)*(g[j].x2-g[j].x1))/((g[i].y2-g[i].y1)*(g[j].x2-g[j].x1)-(g[j].y2-g[j].y1)*(g[i].x2-g[i].x1));//交点横坐标;
//yy=((g[i].y1*g[i].x2-g[i].y2*g[i].x1)*(g[j].y2-g[j].y1)-(g[j].y1*g[j].x2-g[j].y2*g[j].x1)*(g[i].y2-g[i].y1))/((g[j].x2-g[j].x1)*(g[i].y2-g[i].y1)-(g[i].x2-g[i].x1)*(g[j].y2-g[j].y1));//交点纵坐标,其实可以不求纵坐标的;
if(xx>=g[i].x1&&xx<=g[i].x2&&xx>=g[j].x1&&xx<=g[j].x2)
sum++;
}
}
printf("%d\n",sum);
}
return 0;
}