讲解见：http://hi.baidu.com/chinaeli/blog/item/dd00463cdb40eecf9f3d62c7.html

http://blog.163.com/lfw2565295@126/blog/static/12200516201102012251212/

代码：

#include<stdio.h>
#include<math.h>
#include<iostream>
using namespace std;
const int MAXN=1005;
const int MAXM=1000005;
struct Node
{
    int l,r;
}e[MAXN];
struct Node1
{
    int from,to,next;
}edge1[MAXM],edge2[MAXM];
int visit1[MAXN],visit2[MAXN],head1[MAXN],head2[MAXN],Belong[MAXN],T[MAXN];
int tol1,tol2,Bcnt,Tcnt;
void add(int a,int b)
{
    edge1[tol1].from=a;edge1[tol1].to=b;edge1[tol1].next=head1[a];head1[a]=tol1++;
    edge2[tol2].from=b;edge2[tol2].to=a;edge2[tol2].next=head2[b];head2[b]=tol2++;
} 
void dfs1(int x)
{
    int j;
    visit1[x]=1;
    for(j=head1[x];j!=-1;j=edge1[j].next)
       if(visit1[edge1[j].to]==0)  dfs1(edge1[j].to);
    T[Tcnt++]=x;
}           
void dfs2(int x)
{
    int j;
    visit2[x]=1;
    Belong[x]=Bcnt;
    for(j=head2[x];j!=-1;j=edge2[j].next)
       if(visit2[edge2[j].to]==0)  dfs2(edge2[j].to);
}       
double dist(int x1,int y1,int x2,int y2)
{
    return sqrt((double)(x1-x2)*(x1-x2)+(y1-y2)*(y1-y2));
}    
int main()
{
    int i,j,n,m;
    while(scanf("%d%d",&n,&m)!=EOF)
    {
        for(i=0;i<m;i++)
        {
            scanf("%d%d",&e[i].l,&e[i].r);
            /*if(e[i].l>e[i].r)
            {
                int tmp=e[i].l;
                e[i].l=e[i].r;
                e[i].r=e[i].l;
            }  */  //这个可以不加上去 
        }    
        for(i=0;i<2*m;i++)
        {
                head1[i]=-1;
                head2[i]=-1;
                visit1[i]=0;
                visit2[i]=0;
        }    
        tol1=tol2=Bcnt=Tcnt=0;
        for(i=0;i<m;i++)
           for(j=i+1;j<m;j++)
           {
               if((e[i].l<e[j].l&&e[j].l<e[i].r&&e[i].r<e[j].r)||(e[j].l<e[i].l&&e[i].l<e[j].r&&e[j].r<e[i].r))
               {
                   add(2*i,2*j+1);
                   add(2*j+1,2*i);
                   add(2*j,2*i+1);
                   add(2*i+1,2*j);
               }    
           }    
        for(i=0;i<2*m;i++)
             if(visit1[i]==0)  dfs1(i);
        for(i=Tcnt-1;i>=0;i--)
        {
                if(visit2[T[i]]==0)
                {
                    dfs2(T[i]);
                    Bcnt++;
                }    
        }    
        for(i=0;i<=2*m-2;i+=2)
        {
                if(Belong[i]==Belong[i+1])break;
        }    
        if(i>2*m-2) printf("panda is telling the truth...\n");
        else
          printf("the evil panda is lying again\n");

    }    
    return 0;
}