http://uva.onlinejudge.org/index.php?option=com_onlinejudge&Itemid=8&page=show_problem&problem=3587
TwoSAT典例使用
// File Name: uva1146.cpp // Author: bo_jwolf // Created Time: Thursday, May 09, 2013 PM12:10:09 HKT #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include //TwoSAT solver ; using namespace std; const int maxn = 2005 ; //nt n , T[ maxn ][ 2 ] ; /*twosat*/ struct TwoSAT { int n ; vector< int > G[ maxn * 2 ] ; bool mark[ maxn * 2 ]; int S[ maxn * 2 ] , c ; bool dfs( int x ) { if( mark[ x ^ 1 ] ) return false ; if( mark[ x ] ) return true ; mark[ x ] = true ; S[ c++ ] = x; for( int i = 0 ; i < G[x].size() ; i++ ) if( !dfs( G[ x ][ i ] ) ) return false ; return true ; } void init( int n ) { this -> n = n ; for( int i = 0 ; i < n * 2 ; i++ ) G[ i ].clear() ; memset( mark , 0 , sizeof( mark ) ); } void add_clause( int x , int xval , int y , int yval ) { x = x * 2 + xval ; y = y * 2 + yval ; G[ x ^ 1 ].push_back( y ) ; G[ y ^ 1 ].push_back( x ) ; } bool solve() { for( int i = 0 ; i < n * 2 ; i += 2 ) if( !mark[ i ] && !mark[ i + 1 ] ) { c = 0 ; if( !dfs( i ) ) { while( c > 0 ) mark[ S[ --c ] ] = false ; if( !dfs( i + 1 ) ) return false ; } } return true ; } }; TwoSAT solver ; int n , T[ maxn ][ 2 ] ; bool test( int diff ) { solver.init( n ) ; for( int i = 0 ; i < n ; i++ ) for( int a = 0 ; a < 2 ; a++ ) for( int j = i + 1 ; j < n ; j++ ) for( int b = 0 ; b < 2 ; b++ ) if( abs( T[ i ][ a ] - T[ j ][ b ] ) < diff ) solver.add_clause( i , a ^ 1 , j , b ^ 1 ) ; return solver.solve() ; } int main() { while( scanf( "%d" , & n ) == 1 && n ) { int L = 0 , R = 0 ; for( int i = 0 ; i < n ; i++ ) for( int a = 0 ; a < 2 ; a++ ) { scanf( "%d" , &T[ i ][ a ] ) ; R = max( R , T[ i ][ a ] ); } while( L < R ) { int M = L + ( R - L + 1 ) / 2 ; if( test( M ) ) L = M ; else R = M - 1 ; } printf( "%d\n" , L ) ; } return 0; }
