hdu 1853 Cyclic Tour 最小费用最大流

  1 #include<iostream>
  2 #include<cstdio>
  3 #include<cstring>
  4 #include<cstdlib>
  5 #include<cmath>
  6 #include<algorithm>
  7 #include<queue>
  8 #define inf 0x7fffffff
  9 using namespace std;
 10 const int maxn=200+10;
 11 const int M = 40000+100;
 12 
 13 int n,m,from,to;
 14 struct node
 15 {
 16     int v,flow,cost;
 17     int next;
 18 }edge[M*3];
 19 int head[maxn],edgenum;
 20 int dis[maxn],pre[maxn],pid[maxn],vis[maxn];
 21 int Maxflow;
 22 
 23 void add(int u,int v,int flow,int cost)
 24 {
 25     edge[edgenum].v=v ;edge[edgenum].flow=flow ;
 26     edge[edgenum].cost=cost ;edge[edgenum].next=head[u];
 27     head[u]=edgenum++;
 28 
 29     edge[edgenum].v=u ;edge[edgenum].flow=0;
 30     edge[edgenum].cost=-cost ;edge[edgenum].next=head[v];
 31     head[v]=edgenum++;
 32 }
 33 
 34 int spfa()
 35 {
 36     for (int i=1 ;i<=to ;i++) dis[i]=inf;
 37     memset(vis,0,sizeof(vis));
 38     queue<int> Q;
 39     Q.push(from);
 40     dis[from]=0;
 41     vis[from]=1;
 42     while (!Q.empty())
 43     {
 44         int u=Q.front() ;Q.pop() ;
 45         vis[u]=0;
 46         for (int i=head[u] ;i!=-1 ;i=edge[i].next)
 47         {
 48             int v=edge[i].v;
 49             if (edge[i].flow>0 && dis[v]>dis[u]+edge[i].cost)
 50             {
 51                 dis[v]=dis[u]+edge[i].cost;
 52                 pre[v]=u;
 53                 pid[v]=i;
 54                 if (!vis[v])
 55                 {
 56                     vis[v]=1;
 57                     Q.push(v);
 58                 }
 59             }
 60         }
 61     }
 62     return dis[to];
 63 }
 64 
 65 int mincost()
 66 {
 67     int ans=0,maxflow=0;
 68     int aug=0;
 69     while (1)
 70     {
 71         aug=inf;
 72         int tmp=spfa();
 73         if (tmp==inf) break;
 74         for (int i=to ;i!=from ;i=pre[i])
 75         {
 76             if (edge[pid[i] ].flow<aug)
 77                 aug=edge[pid[i] ].flow;
 78         }
 79         for (int i=to ;i!=from ;i=pre[i])
 80         {
 81             edge[pid[i] ].flow -= aug;
 82             edge[pid[i]^1 ].flow += aug;
 83         }
 84         maxflow += aug;
 85         ans += tmp*aug;
 86     }
 87     Maxflow=maxflow;
 88     return ans;
 89 }
 90 
 91 int main()
 92 {
 93     while (scanf("%d%d",&n,&m)!=EOF)
 94     {
 95         memset(head,-1,sizeof(head));
 96         edgenum=0;
 97         int a,b,c;
 98         from=2*n+1;
 99         to=from+1;
100         Maxflow=0;
101         for (int i=0 ;i<m ;i++)
102         {
103             scanf("%d%d%d",&a,&b,&c);
104             add(a,b+n,1,c);
105         }
106         for (int i=1 ;i<=n ;i++)
107         {
108             add(from,i,1,0);
109             add(i+n,to,1,0);
110         }
111         int ans=mincost();
112         printf("%d\n",Maxflow==n ? ans : -1);
113     }
114     return 0;
115 }