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 ;
}
