i don't really sure if i understand the problem correctly , but his is my
program. plase have a look

#include <stdio.h>
#include <stdlib.h>
struct co {
 double x,y;
 int id;
};
 int cmp(const void *a, const void *b) {
 co p=*((co *)a);
 co q=*((co *)b);
 double result=p.x*q.y-p.y*q.x;
  if (result>0)
   return 1;
  else if (result<0)
   return -1;
  else
   return 0;
 }

void main() {
const int maxsize=10000;
co p[maxsize];
int i,j,k;
int size;
#ifndef ONLINE_JUDGE
freopen("1207.in","r",stdin);
freopen("1207.out","w",stdout);
#endif
 scanf("%d",&size);
 for (i=0; i<size; i++) {
  scanf("%lf%lf",&(p[i].x),&(p[i].y));
  p[i].id=i+1;
 }
 qsort(p,size,sizeof(co),cmp);
 printf("%d %d",p[0].id,p[size/2].id);
}

4
1 1
2 2
1 0
2 0

> 4
> 1 1
> 2 2
> 1 0
> 2 0
my program output is 3 2 , what's the correct one and why?

it seems like I really misunderstand the problem and I don't know what's
the point :(

Hmm, that's strange. 3 2 is ok, but on my computer it returns 2 4,
what is of course wrong. I guess it depends on the realization of
qsort. IMHO, your solution is not ok, but I'm not sure. What compiler
do you use?

quite strange , I use Mingw as compiler, it produces correct answer

anyway, my old this solution is wrong as you said

> i don't really sure if i understand the problem correctly , but his
is my
> program. plase have a look
>
> #include <stdio.h>
> #include <stdlib.h>
> struct co {
>  double x,y;
>  int id;
> };
>  int cmp(const void *a, const void *b) {
>  co p=*((co *)a);
>  co q=*((co *)b);
>  double result=p.x*q.y-p.y*q.x;
>   if (result>0)
>    return 1;
>   else if (result<0)
>    return -1;
>   else
>    return 0;
>  }
>
> void main() {
> const int maxsize=10000;
> co p[maxsize];
> int i,j,k;
> int size;
> #ifndef ONLINE_JUDGE
> freopen("1207.in","r",stdin);
> freopen("1207.out","w",stdout);
> #endif
>  scanf("%d",&size);
>  for (i=0; i<size; i++) {
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!1111
>   scanf("%lf%lf",&(p[i].x),&(p[i].y));
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! (*)
>   p[i].id=i+1;
>  }
>  qsort(p,size,sizeof(co),cmp);
>  printf("%d %d",p[0].id,p[size/2].id);
> }

(*) I think the coordinates must be shifted, because the point 0
must be (0, 0) (basis)

Edited by author 27.05.2004 21:25

ss