POJ3207+tarjan+2-sat

  1 /*

  2 2-sat

  3 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。

  4     问有没有可能所有的线画完 且 不出现相交。

  5 思路：把线画在圆内或圆外 看成一个组合。其它的则建边。

  6 */

  7 #include<stdio.h>

  8 #include<string.h>

  9 #include<stdlib.h>

 10 #include<math.h>

 11 #include<algorithm>

 12 #include<iostream>

 13 #include<set>

 14 #include<stack>

 15 #include<queue>

 16 #include<map>

 17 #include<vector>

 18 using namespace std;

 19 

 20 typedef long long int64;

 21 //typedef __int64 int64;

 22 typedef pair<int64,int64> PII;

 23 #define MP(a,b) make_pair((a),(b)) 

 24 const int maxn = 2225;

 25 const int maxm = 250000;

 26 const int inf = 0x7fffffff;

 27 const double pi=acos(-1.0);

 28 const double eps = 1e-8;

 29 

 30 struct Edge{

 31     int u,v,next;

 32 }edge[ maxm*2+5 ];

 33 int cnt,head[ maxn ];

 34 int vis[ maxn ];

 35 int dfn[ maxn ],low[ maxn ];

 36 int belong[ maxn ],Cnt,id;

 37 stack<int>s;

 38 struct EDGE{

 39     int l,r;

 40 }E[ maxn ];

 41 

 42 void init(){

 43     id = Cnt = 0;

 44     cnt = 0;

 45     while( !s.empty() )

 46         s.pop();

 47     memset( head,-1,sizeof( head ) );

 48     memset( vis,-1,sizeof( vis ) );

 49     memset( dfn,-1,sizeof( dfn ) );

 50     memset( low,-1,sizeof( low ) );

 51 }

 52 

 53 void addedge( int a,int b ){

 54     edge[ cnt ].u = a;

 55     edge[ cnt ].v = b;

 56     edge[ cnt ].next = head[ a ];

 57     head[ a ] = cnt++;

 58 }

 59 

 60 bool ok( int L,int R ){

 61     int x1 = E[L].l;

 62     int y1 = E[L].r;

 63     int x2 = E[R].l;

 64     int y2 = E[R].r;

 65     if( x2>x1&&x2<y1 ){

 66         if( y2>=y1 ) return true;

 67         if( y2<=x1 ) return true;

 68     }

 69     if( y2>x1&&y2<y1 ){

 70         if( x2>=y1 ) return true;

 71         if( x2<=x1 ) return true;

 72     }

 73     return false;

 74 }

 75 

 76 void tarjan( int cur ){

 77     dfn[ cur ] = low[ cur ] = id++;

 78     vis[ cur ] = 1;

 79     s.push( cur );

 80     for( int i=head[ cur ];i!=-1;i=edge[i].next ){

 81         int nxt = edge[ i ].v;

 82         if( dfn[ nxt ]==-1 ){

 83             tarjan( nxt );

 84             low[ cur ] = min( low[ cur ],low[ nxt ] );

 85         }

 86         else if( vis[ nxt ]==1 ){

 87             low[ cur ] = min( low[ cur ],dfn[ nxt ] );

 88         }

 89     }

 90     if( dfn[ cur ]==low[ cur ] ){

 91         Cnt ++;

 92         while( 1 ){

 93             int tmp = s.top();

 94             s.pop();

 95             vis[ tmp ] = 0;

 96             belong[ tmp ] = Cnt;

 97             if( tmp==cur ) break;

 98         }

 99     }

100 }

101 

102 int main(){

103     int n,m;

104     while( scanf("%d%d",&n,&m)==2 ){

105         init();

106         int a,b;

107         for( int i=1;i<=m;i++ ){

108             scanf("%d%d",&a,&b);

109             a++,b++;

110             E[ i ].l = min( a,b );

111             E[ i ].r = max( a,b );

112         }

113         for( int i=1;i<=m;i++ ){

114             for( int j=i+1;j<=m;j++ ){

115                 if( ok( i,j )==true ){

116                     addedge( i,j+m );

117                     addedge( j+m,i );

118                     addedge( i+m,j );

119                     addedge( j,i+m );

120                 }

121             }

122         }//build mat

123         for( int i=1;i<=2*m;i++ ){

124             if( dfn[i]==-1 ){

125                 tarjan( i );

126             }

127         }

128         //

129         bool f = true;

130         for( int i=1;i<=m;i++ ){

131             if( belong[i]==belong[i+m] ){

132                 f = false;

133                 break;

134             }

135         }

136         if( f==false ) printf("the evil panda is lying again");

137         else printf("panda is telling the truth...");

138         printf("\n");

139     }

140     return 0;

141 }

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