hdu 2485 Destroying the bus stations 最小费用最大流

  1 #include<iostream>
  2 #include<cstdio>
  3 #include<cstring>
  4 #include<algorithm>
  5 using namespace std;
  6 const int N =110, M=10010,INF=0x3f3f3f3f;
  7 struct node
  8 {
  9     int to, next, c ,f;//c是容量，f是费用
 10 }edge[M];
 11 int head[N],dis[N],load[N],p[N];
 12 bool vis[N];
 13 int tot,flow,ans,D;
 14 bool spfa(int S, int E,int n)
 15 {
 16     int que[N*10],qout,qin;
 17     memset(vis,0,sizeof(vis));
 18     memset(load,-1,sizeof(load));
 19     memset(p,-1,sizeof(p));
 20     for(int i=0;i<=n;i++)
 21         dis[i]=INF;
 22     qin=qout=0;
 23     que[qin++]=S;
 24     dis[S]=0;
 25     vis[S]=1;
 26     while(qin!=qout)
 27     {
 28         int u=que[qout++];
 29         vis[u]=0;
 30         for(int i=head[u];i!=-1;i=edge[i].next)
 31         {
 32             if(edge[i].c)
 33             {
 34                 int v=edge[i].to;
 35                 if(dis[v]-dis[u]>edge[i].f)
 36                 {
 37                     dis[v]=dis[u]+edge[i].f;
 38                     p[v]=u;
 39                     load[v]=i;
 40                     if(!vis[v])
 41                     {
 42                         vis[v]=1;
 43                         que[qin++]=v;
 44                     }
 45                 }
 46             }
 47         }
 48     }
 49     if(dis[E]>D) return 0;
 50     return 1;
 51 }
 52 void MCF(int S, int E,int n)
 53 {
 54     int u,mn;
 55     flow=ans=0;
 56     while(spfa(S,E,n))
 57     {
 58         u=E; mn=INF;
 59         while(p[u]!=-1)
 60         {
 61             mn=min(edge[load[u]].c, mn);
 62             u=p[u];
 63         }
 64         u=E;
 65         while(p[u]!=-1)
 66         {
 67             edge[load[u]].c-=mn;
 68             edge[load[u]^1].c+=mn;
 69             u=p[u];
 70         }
 71         ans+=dis[E]*mn;
 72         flow+=mn;
 73     }
 74 }
 75 void addedge(int a,int b,int c,int d)
 76 {
 77     edge[tot].to=b;edge[tot].c=c;edge[tot].f=d;
 78     edge[tot].next=head[a];head[a]=tot++;
 79     edge[tot].to=a;edge[tot].c=0;edge[tot].f=-d;
 80     edge[tot].next=head[b];head[b]=tot++;
 81 }
 82 void init()
 83 {
 84     tot=0;
 85     memset(head,-1,sizeof(head));
 86 }
 87 int main()
 88 {
 89     //freopen("test.txt","r",stdin);
 90     int n,m,i,j,k;
 91     while(scanf("%d%d%d",&n,&m,&D)!=EOF&&n)
 92     {
 93         init();
 94         while(m--)
 95         {
 96             scanf("%d%d",&i,&j);
 97             if(i!=1) addedge(i+n,j,INF,1);
 98             else addedge(i,j,INF,1);
 99         }
100         for(i=2;i<n;i++) addedge(i,i+n,1,0);
101         MCF(1,n,2*n);
102         printf("%d\n",flow);
103     }
104     return 0;
105 }