利用叉积解方程
#include <cstdio>
#define MAX 1<<31
#define dd double
int xmult(dd x1,dd y1,dd x2,dd y2,dd x,dd y){
return (x1-x)*(y2-y)-(x2-x)*(y1-y);
}
int main(){
int n;
dd x1,y1,x2,y2,x3,y3,x4,y4;
scanf("%d",&n);
puts("INTERSECTING LINES OUTPUT");
while(n--){
scanf("%lf%lf%lf%lf%lf%lf%lf%lf",&x1,&y1,&x2,&y2,&x3,&y3,&x4,&y4);
dd a1=y1-y2;
dd b1=x2-x1;
dd c1=xmult(x1,y1,x2,y2,0,0);
dd a2=y3-y4;
dd b2=x4-x3;
dd c2=xmult(x3,y3,x4,y4,0,0);
if(a1*b2==a2*b1){
if(xmult(x1,y1,x2,y2,x3,y3)==0)
puts("LINE");
else puts("NONE");
}
else {
dd cx,cy;
cx=(b1*c2-c1*b2)/(a1*b2-a2*b1);
cy=(a1*c2-c1*a2)/(b1*a2-b2*a1);
printf("POINT %.2f %.2f\n",cx,cy);
}
}
puts("END OF OUTPUT");
}
利用点斜式解方程
#include <cstdio>
#define MAX 1<<31
#define dd double
struct P{
dd x,y;
void input(){
scanf("%lf%lf",&x,&y);
}
void output(){
printf("POINT %.2f %.2f\n",x,y);
}
};
struct L{
P s,e;
void input(){
s.input(),e.input();
}
dd k(){
if(s.x==e.x)return MAX;
return (s.y-e.y)/(s.x-e.x);
}
}l1,l2;
int xmult(P a,P b,P o){
return (a.x-o.x)*(b.y-o.y)-(b.x-o.x)*(a.y-o.y);
}
void getCross(L a,L b){
P c;
dd ka=a.k(),kb=b.k();
if(ka==MAX){//a是竖直的
c.x=a.s.x;
c.y=(c.x-b.s.x)*kb+b.s.y;
}
else{
if(kb==MAX)
c.x=b.s.x;
else
c.x=(a.s.y-b.s.y-ka*a.s.x+kb*b.s.x)/(kb-ka);
c.y=(c.x-a.s.x)*ka+a.s.y;
}
c.output();
}
int main(){
int n;
scanf("%d",&n);
puts("INTERSECTING LINES OUTPUT");
while(n--){
l1.input(),l2.input();
dd ka=l1.k(),kb=l2.k();
if(ka==kb){
if(xmult(l1.s,l1.e,l2.s)==0)
puts("LINE");
else puts("NONE");
}
else
getCross(l1,l2);
}
puts("END OF OUTPUT");
}