POJ3207+Tarjan+2-sat

/*2-sat題意：給定一個圓，圓上一些點。兩點一線。現給出一些線，這些線可以在圓內連起來，也可以在圓外。問有沒有可能所有的線畫完 且 不出現相交。思路：把線畫在圓內或圓外 看成一個組合。其它的則建邊。*/#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 matfor( 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("\n");}return 0;}