HDU3549(Flow Problem)(网络最大流)

  
    

   
     赤裸裸的Ford-Fulkerson算法求最大流。
  
    
  
    

   
     

  
    
  
    

   
     #include 
   
     <
   
     iostream
   
     >
   
     
#include 
   
     <
   
     cstring
   
     >
   
     
#include 
   
     <
   
     queue
   
     >
   
     


   
     using
   
      
   
     namespace
   
      std;

   
     const
   
      
   
     int
   
      MAX 
   
     =
   
      
   
     1003
   
     ;

   
     int
   
      map[MAX][MAX],pre[MAX],n,m,ans;

   
     bool
   
      vis[MAX];


   
     int
   
      Maxflow()　　　　//　　采用BFS找增广路径
{
 
   
     while
   
     (
   
     true
   
     )
 {
 queue
   
     <
   
     int
   
     >
   
      que;
 memset(pre,
   
     0
   
     ,
   
     sizeof
   
     (pre));
 memset(vis,
   
     0
   
     ,
   
     sizeof
   
     (vis));
 vis[
   
     1
   
     ] 
   
     =
   
      
   
     true
   
     ; que.push(
   
     1
   
     );

 
   
     while
   
     (
   
     !
   
     que.empty())
 {
 
   
     int
   
      cur 
   
     =
   
      que.front(); que.pop();

 
   
     if
   
     (cur 
   
     ==
   
      n) 
   
     break
   
     ;　　//　　表明已找到一条增广路径

 
   
     for
   
     (
   
     int
   
      i 
   
     =
   
      
   
     1
   
     ;i 
   
     <=
   
      n;
   
     ++
   
     i)
 {
 
   
     if
   
     (
   
     !
   
     vis[i] 
   
     &&
   
      map[cur][i])
 {
 que.push(i); pre[i] 
   
     =
   
      cur;
 vis[i] 
   
     =
   
      
   
     true
   
     ;
 }
 }
 }

 
   
     if
   
     (
   
     !
   
     vis[n]) 
   
     break
   
     ;　　　　//　　无法找到增广路径

 
   
     int
   
      Min 
   
     =
   
      
   
     100000000
   
     ;

 
   
     for
   
     (
   
     int
   
      u 
   
     =
   
      n;u 
   
     !=
   
      
   
     1
   
     ;u 
   
     =
   
      pre[u])
 {
 
   
     if
   
     (Min 
   
     >
   
      map[pre[u]][u]) Min 
   
     =
   
      map[pre[u]][u];
 }

 
   
     for
   
     (u 
   
     =
   
      n;u 
   
     !=
   
      
   
     1
   
     ;u 
   
     =
   
      pre[u])
 {
 map[pre[u]][u] 
   
     -=
   
      Min;
 map[u][pre[u]] 
   
     +=
   
      Min;
 }
 ans 
   
     +=
   
      Min;
 }

 
   
     return
   
      ans;
}



   
     int
   
      main()
{
 
   
     //
   
     freopen("hdu.txt","r",stdin);
   
     

   
      
   
     int
   
      u,v,d,t,i,j;

 cin
   
     >>
   
     t;

 
   
     for
   
     (
   
     int
   
      ca 
   
     =
   
      
   
     1
   
     ;ca 
   
     <=
   
      t;
   
     ++
   
     ca)
 {
 
   
     //
   
      cin>>n>>m;
   
     

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

 
   
     for
   
     (i 
   
     =
   
      
   
     1
   
     ;i 
   
     <=
   
      n;
   
     ++
   
     i)
 {
 
   
     for
   
     (j 
   
     =
   
      
   
     1
   
     ;j 
   
     <=
   
      n;
   
     ++
   
     j) map[i][j] 
   
     =
   
      
   
     0
   
     ;
 }

 
   
     for
   
     (i 
   
     =
   
      
   
     0
   
     ;i 
   
     <
   
      m;
   
     ++
   
     i)
 {
 
   
     //
   
      cin>>u>>v>>d;
   
     

   
      scanf(
   
     "
   
     %d %d %d
   
     "
   
     ,
   
     &
   
     u,
   
     &
   
     v,
   
     &
   
     d);
 map[u][v] 
   
     +=
   
      d;
 }

 ans 
   
     =
   
      
   
     0
   
     ;
 Maxflow();

 cout
   
     <<
   
     "
   
     Case 
   
     "
   
     <<
   
     ca
   
     <<
   
     "
   
     : 
   
     "
   
     <<
   
     ans
   
     <<
   
     endl;
 }

 
   
     return
   
      
   
     0
   
     ;
}