BZOJ-1027: [JSOI2007]合金（最小环）

题目：http://www.lydsy.com/JudgeOnline/problem.php?id=1027

额。。。计算几何太弱了，这题搞了N久才A掉，就是用最小环求一下最小的凸包，然后记得要特判一下所有点都在一个点处的情况。。。

代码：

#include 

#include 

#include 

#include 

#include 

#include 

 

using namespace std ;

 

const int inf = 1000000 ;

const double esp = 0.00000000001 ;

const int maxn = 510 ;

 

struct Point {

    double x , y ;

    void read(  ) {

        scanf( "%lf%lf" , &x , &y ) ;

    }

} p0[ maxn ] , p1[ maxn ] ;

 

struct Vector {

    double x , y ;

} ;

 

Vector operator - ( const Point &x , const Point &y ) {

    return ( Vector ) { x.x - y.x , x.y - y.y } ;

}

 

double operator * ( const Vector &x , const Vector &y ) {

    return x.x * y.y - y.x * x.y ;

}

 

double mul( const Vector &x , const Vector &y ) {

    return x.x * y.x + x.y * y.y ;

}

 

struct graph {

     

    vector < int > E[ maxn ] ;

    int V ;

     

    void Init( int _V ) {

        V = _V ;

    }

     

    void addedge( int s , int t ) {

        E[ s ].push_back( t ) ;

    }

     

    int dist[ maxn ] ;

    queue < int > q ;

     

    void bfs( int v ) {

        for ( int i = 0 ; i ++ < V ; ) dist[ i ] = inf ;

        for ( vector < int > :: iterator p = E[ v ].begin(  ) ; p != E[ v ].end(  ) ; ++ p ) {

            dist[ *p ] = 1 , q.push( *p ) ;

        }

        while ( ! q.empty(  ) ) {

            int now = q.front(  ) ; q.pop(  ) ;

            for ( vector < int > :: iterator p = E[ now ].begin(  ) ; p != E[ now ].end(  ) ; ++ p ) if ( dist[ now ] + 1 < dist[ *p ] ) {

                dist[ *p ] = dist[ now ] + 1 ;

                q.push( *p ) ;

            }

        }

    }

     

} g ;

 

int n , m ;

 

bool cmp( double x , double y ) {

    return abs( x - y ) < esp ;

}

 

int main(  ) {

    scanf( "%d%d" , &n , &m ) ;

    for ( int i = 0 ; i ++ < n ; ) {

        p0[ i ].read(  ) ;

        double x ; scanf( "%lf" , &x ) ;

    }

    bool flag = true ;

    for ( int i = 0 ; i ++ < m ; ) {

        p1[ i ].read(  ) ;

        double x ; scanf( "%lf" , &x ) ;

        if ( ! ( cmp( p1[ i ].x , p1[ 1 ].x ) && cmp( p1[ i ].y , p1[ 1 ].y ) ) ) flag = false ;

    }

    if ( flag ) {

        for ( int i = 0 ; i ++ < n ; ) if ( cmp( p0[ i ].x , p1[ 1 ].x ) && cmp( p0[ i ].y , p1[ 1 ].y ) ) {

            printf( "1\n" ) ;

            return 0 ;

        }

    }

    g.Init( n ) ;

    for ( int i = 0 ; i ++ < n ; ) for ( int j = 0 ; j ++ < n ; ) if ( i != j ) {

        Vector v = p0[ j ] - p0[ i ] ;

        flag = true ;

        for ( int k = 0 ; k ++ < m ; ){

            double ret = v * ( p1[ k ] - p0[ i ] ) ;

            if ( ! ( ret > esp || ( ret > - esp && ret < esp && mul( p1[ k ] - p0[ i ] , p1[ k ] - p0[ j ] ) < esp ) ) ) {

                flag = false ;

                break ;

            }

        }

        if ( flag ) g.addedge( i , j ) ;

    }

    int ans = inf ;

    for ( int i = 0 ; i ++ < n ; ) {

        g.bfs( i ) ;

        ans = min( ans , g.dist[ i ] ) ;

    }

    printf( "%d\n" , ans < inf ? ans : -1 ) ;

    return 0 ;

}