BZOJ-1266: [AHOI2006]上学路线route(最短路+最小割)

题目:http://www.lydsy.com/JudgeOnline/problem.php?id=1266

按题意跑一次SPFA之后再建最短路图,然后跑一次最小流求最小割即可。

代码:

#include <cstdio>

#include <algorithm>

#include <cstring>

#include <deque>

 

using namespace std ;

 

#define MAXV 1010

#define pb push_back

#define pf push_front

#define MAXM 150010

#define inf 0x7fffffff

#define MAXN 1010

 

struct network {

         

    struct edge {

        edge *next , *pair ;

        int t , f ;

    } *head[ MAXV ] ;

         

    void Add( int s , int t , int f ) {

        edge *p = new( edge ) ;

        p -> t = t , p -> f = f , p -> next = head[ s ] ;

        head[ s ] = p ;

    }

         

    void AddEdge( int s , int t , int f ) {

        Add( s , t , f ) , Add( t , s , 0 ) ;

        head[ s ] -> pair = head[ t ] , head[ t ] -> pair = head[ s ] ;

    }

         

    int S , T ;

         

    network(  ) {

        memset( head , 0 , sizeof( head ) ) ;

    }

         

    int h[ MAXV ] , gap[ MAXV ] ;

    edge *d[ MAXV ] ;

         

    int sap( int v , int flow ) {

        if ( v == T ) return flow ;

        int rec = 0 ;

        for ( edge *p = d[ v ] ; p ; p = p -> next ) if ( p -> f && h[ v ] == h[ p -> t ] + 1 ) {

            int ret = sap( p -> t , min( flow - rec , p -> f ) ) ;

            p -> f -= ret , p -> pair -> f += ret , d[ v ] = p ;

            if ( ( rec += ret ) == flow ) return flow ;

        }

        if ( ! ( -- gap[ h[ v ] ] ) ) h[ S ] = T ;

        gap[ ++ h[ v ] ] ++ , d[ v ] = head[ v ] ;

        return rec ;

    }

         

    int maxflow(  ) {

        int flow = 0 ;

        memset( h , 0 , sizeof( h ) ) ;

        memset( gap , 0 , sizeof( gap ) ) ;

        for ( int i = 0 ; i ++ < T ; ) d[ i ] = head[ i ] ;

        gap[ S ] = T ;

        while ( h[ S ] < T ) flow += sap( S , inf ) ;

        return flow ;

    }

         

} net ;

 

struct graph {

     

    struct edge {

        edge *next ;

        int t , d , c ;

    } *head[ MAXN ] ;

     

    int n ;

     

    graph(  ) {

        memset( head , 0 , sizeof( head ) ) ;

    }

     

    void Add( int s , int t , int d ) {

        edge *p = new( edge ) ;

        p -> t = t , p -> d = d , p -> next = head[ s ] ;

        head[ s ] = p ;

    }

     

    void AddEdge( int s , int t , int d ) {

        Add( s , t , d ) , Add( t , s , d ) ;

    }

     

    deque < int > q ;

    int dist[ MAXN ] ;

    bool f[ MAXN ] ;

     

    void spfa( int S ) {

        memset( f , false , sizeof( f ) ) ;

        q.clear(  ) ;

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

        q.pf( S ) , dist[ S ] = 0 , f[ S ] = true ;

        while ( ! q.empty(  ) ) {

            int v = q.front(  ) ; q.pop_front(  ) , f[ v ] = false ;

            for ( edge *p = head[ v ] ; p ; p = p -> next ) {

                if ( dist[ p -> t ] > dist[ v ] + p -> d ) {

                    dist[ p -> t ] = dist[ v ] + p -> d ;

                    if ( ! f[ p -> t ] ) {

                        f[ p -> t ] = true ;

                        if ( ! q.empty(  ) && dist[ q.front(  ) ] > dist[ p -> t ] ) {

                            q.pf( p -> t ) ;

                        } else q.pb( p -> t ) ;

                    }

                }

            }

        }

    }

     

} g ;

 

int e[ MAXM ][ 4 ] , n , m ;

 

int main(  ) {

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

    g.n = n ;

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

        scanf( "%d%d%d%d" , &e[ i ][ 0 ] , &e[ i ][ 1 ] , &e[ i ][ 2 ] , &e[ i ][ 3 ] ) ;

        g.AddEdge( e[ i ][ 0 ] , e[ i ][ 1 ] , e[ i ][ 2 ] ) ;

    }

    g.spfa( 1 ) ;

    printf( "%d\n" , g.dist[ n ] ) ;

    net.S = 1 , net.T = n ;

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

        if ( g.dist[ e[ i ][ 1 ] ] == g.dist[ e[ i ][ 0 ] ] + e[ i ][ 2 ] ) {

            net.AddEdge( e[ i ][ 0 ] , e[ i ][ 1 ] , e[ i ][ 3 ] ) ;

        }

        if ( g.dist[ e[ i ][ 0 ] ] == g.dist[ e[ i ][ 1 ] ] + e[ i ][ 2 ] ) {

            net.AddEdge( e[ i ][ 1 ] , e[ i ][ 0 ] , e[ i ][ 3 ] ) ;

        }

    }

    printf( "%d\n" , net.maxflow(  ) ) ;

    return 0 ;

}
    原文作者:AmadeusChan
    原文地址: https://www.jianshu.com/p/800f84301338
    本文转自网络文章,转载此文章仅为分享知识,如有侵权,请联系博主进行删除。
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