my code :

#include <iostream>
#include <algorithm>

using namespace std;

struct cord
{
  int x,y,p;
};

int comp(cord a,cord b)
{
  if (a.x < b.x) return 1;
  return 0;
}

int main()
{
    cord a[501];
    int best[501];
    int way[501];
    int oway[501],f=0;
    int n,i,j,k,l;

    cin>>n;
    for (i=0;i<n;i++)
     {
      cin>>a[i].x>>a[i].y;
      if (a[i].y < a[i].x)
       swap(a[i].x,a[i].y);
      best[i]=1; a[i].p=i+1;
      way[i]=i;
     }
    sort(a,a+n,comp);
    for (i=0;i<n;i++)
     for (j=0;j<n;j++)
      if (j != i)
       {
         if (a[i].x >= a[j].x && a[i].y <= a[j].y)
          {
            if (best[j]+1 >= best[i])
             {
              best[i]=best[j]+1;
              way[i]=j;
             }
          }
       }
    k=best[0]; l=0;
    for (i=1;i<n;i++)
     if (best[i] >= k) k=best[i],l=i;
    while (l != way[l] && k > 0)
     {
      oway[f]=a[l].p; f++;
      l=way[l]; k--;
        }
    oway[f]=a[l].p; f++;
    cout<<f<<endl;
    for (i=0;i<f;i++) cout<<oway[i]<<" ";
    cout<<endl;

    return 0;
}

Edited by author 26.04.2011 18:15

Edited by author 26.04.2011 18:15

oh, I have solved it. Thanks!

Edited by author 26.04.2011 23:09

Why?