HDU 4411 Arrest

http://www.cnblogs.com/jianglangcaijin/archive/2012/09/24/2700509.html

思路:

S->0 流量为K费用0

0->i 流量为inf,费用为a[0][i]

0->T 流量为K，费用0

i->i+n 流量为1,费用为-inf

i+n->T 流量为1，费用为a[0][i]

 #include<algorithm>
 #include<cstdio>
 #include<cmath>
 #include<cstring>
 #include<iostream>
 #define inf 1000000
 int a[][],K;
 int tot,go[],next[],first[],cost[],flow[];
 int op[],dis[],c[],vis[],edge[],from[];
 int S,T,n,m,ans;
 int read(){
     char ch=getchar();int t=,f=;
     while (ch<''||ch>''){if (ch=='-') f=-;ch=getchar();}
     while (''<=ch&&ch<=''){t=t*+ch-'';ch=getchar();}
     return t*f;
 }
 void insert(int x,int y,int z,int l){
     tot++;
     go[tot]=y;
     next[tot]=first[x];
     first[x]=tot;
     flow[tot]=z;
     cost[tot]=l;
 }
 void add(int x,int y,int z,int l){
     insert(x,y,z,l);op[tot]=tot+;
     insert(y,x,,-l);op[tot]=tot-;
 }
 bool spfa(){
     for (int i=;i<=T;i++)
      dis[i]=0x3f3f3f3f,vis[i]=;
     int h=,t=;c[]=S;vis[S]=;dis[S]=;
     while (h<=t){
         int now=c[h++];
         for (int i=first[now];i;i=next[i]){
             int pur=go[i];
             if (dis[pur]>dis[now]+cost[i]&&flow[i]){
                 dis[pur]=dis[now]+cost[i];
                 edge[pur]=i;
                 from[pur]=now;
                 if (vis[pur]) continue;
                 vis[pur]=;
                 c[++t]=pur;
             }
         }
         vis[now]=;
     }
     return dis[T]!=0x3f3f3f3f;
 }
 void updata(){
     int mn=0x3f3f3f3f;
     for (int i=T;i!=S;i=from[i]){
         mn=std::min(mn,flow[edge[i]]);
     }
     for (int i=T;i!=S;i=from[i]){
         ans+=mn*cost[edge[i]];
         flow[edge[i]]-=mn;
         flow[op[edge[i]]]+=mn;
     }
 }
 int main(){
     while (scanf("%d",&n)!=EOF){
         m=read();K=read();
         if (n==&&K==&&m==) return ;
         for (int i=;i<=T;i++) first[i]=;tot=;
         S=*n+;T=S+;
         for (int i=;i<=n;i++)
          for (int j=;j<=n;j++)
           if (i==j) a[i][j]=;
           else a[i][j]=0x3f3f3f3f;
         while(m--){
             int u=read(),v=read(),w=read();
             a[u][v]=std::min(a[u][v],w);
             a[v][u]=std::min(a[v][u],w);
         }
         for (int k=;k<=n;k++)
          for (int i=;i<=n;i++)
           for (int j=;j<=n;j++)
            a[i][j]=std::min(a[i][j],a[i][k]+a[k][j]);
         add(S,,K,);
         add(,T,K,);
         for (int i=;i<=n;i++)
          if (a[][i]<0x3f3f3f3f)
           add(,i,inf,a[][i]);
         for (int i=;i<=n;i++)
          for (int j=i+;j<=n;j++)
           if (a[i][j]<0x3f3f3f3f)
            add(i+n,j,,a[i][j]);
         for (int i=;i<=n;i++)
           if (a[][i]<0x3f3f3f3f)
            add(i+n,T,,a[][i]);
         for (int i=;i<=n;i++)
          add(i,i+n,,-inf);
         ans=inf*n;
         while (spfa()) updata();
         printf("%d\n",ans);
     }
 }