POJ3207+tarjan+2-sat

/*
2-sat
题意：给定一个圆，圆上一些点。两点一线。现给出一些线，这些线可以在圆内连起来，也可以在圆外。
    问有没有可能所有的线画完 且 不出现相交。
思路：把线画在圆内或圆外 看成一个组合。其它的则建边。
*/
#include<stdio.h>
#include<string.h>
#include<stdlib.h>
#include<math.h>
#include<algorithm>
#include<iostream>
#include<set>
#include<stack>
#include<queue>
#include<map>
#include<vector>
using namespace std;

typedef long long int64;
//typedef __int64 int64;
typedef pair<int64,int64> PII;
#define MP(a,b) make_pair((a),(b)) 
const int maxn = 2225;
const int maxm = 250000;
const int inf = 0x7fffffff;
const double pi=acos(-1.0);
const double eps = 1e-8;

struct Edge{
    int u,v,next;
}edge[ maxm*2+5 ];
int cnt,head[ maxn ];
int vis[ maxn ];
int dfn[ maxn ],low[ maxn ];
int belong[ maxn ],Cnt,id;
stack<int>s;
struct EDGE{
    int l,r;
}E[ maxn ];

void init(){
    id = Cnt = 0;
    cnt = 0;
    while( !s.empty() )
        s.pop();
    memset( head,-1,sizeof( head ) );
    memset( vis,-1,sizeof( vis ) );
    memset( dfn,-1,sizeof( dfn ) );
    memset( low,-1,sizeof( low ) );
}

void addedge( int a,int b ){
    edge[ cnt ].u = a;
    edge[ cnt ].v = b;
    edge[ cnt ].next = head[ a ];
    head[ a ] = cnt++;
}

bool ok( int L,int R ){
    int x1 = E[L].l;
    int y1 = E[L].r;
    int x2 = E[R].l;
    int y2 = E[R].r;
    if( x2>x1&&x2<y1 ){
        if( y2>=y1 ) return true;
        if( y2<=x1 ) return true;
    }
    if( y2>x1&&y2<y1 ){
        if( x2>=y1 ) return true;
        if( x2<=x1 ) return true;
    }
    return false;
}

void tarjan( int cur ){
    dfn[ cur ] = low[ cur ] = id++;
    vis[ cur ] = 1;
    s.push( cur );
    for( int i=head[ cur ];i!=-1;i=edge[i].next ){
        int nxt = edge[ i ].v;
        if( dfn[ nxt ]==-1 ){
            tarjan( nxt );
            low[ cur ] = min( low[ cur ],low[ nxt ] );
        }
        else if( vis[ nxt ]==1 ){
            low[ cur ] = min( low[ cur ],dfn[ nxt ] );
        }
    }
    if( dfn[ cur ]==low[ cur ] ){
        Cnt ++;
        while( 1 ){
            int tmp = s.top();
            s.pop();
            vis[ tmp ] = 0;
            belong[ tmp ] = Cnt;
            if( tmp==cur ) break;
        }
    }
}

int main(){
    int n,m;
    while( scanf("%d%d",&n,&m)==2 ){
        init();
        int a,b;
        for( int i=1;i<=m;i++ ){
            scanf("%d%d",&a,&b);
            a++,b++;
            E[ i ].l = min( a,b );
            E[ i ].r = max( a,b );
        }
        for( int i=1;i<=m;i++ ){
            for( int j=i+1;j<=m;j++ ){
                if( ok( i,j )==true ){
                    addedge( i,j+m );
                    addedge( j+m,i );
                    addedge( i+m,j );
                    addedge( j,i+m );
                }
            }
        }//build mat
        for( int i=1;i<=2*m;i++ ){
            if( dfn[i]==-1 ){
                tarjan( i );
            }
        }
        //
        bool f = true;
        for( int i=1;i<=m;i++ ){
            if( belong[i]==belong[i+m] ){
                f = false;
                break;
            }
        }
        if( f==false ) printf("the evil panda is lying again");
        else printf("panda is telling the truth...");
        printf("
");
    }
    return 0;
}