费用流模板（最大流最小费用）—————————————————————————–
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namespace MinCostFlow { int tot,S,T,Next[M],head[N],tree[M],val[M],Cost[M],From[M],Prev[N],FLOW,dis[N],Queue[N*2]; bool visit[N]; void add(int x,int y,int z,int d) { tot++; Next[tot]=head[x]; head[x]=tot; tree[tot]=y; val[tot]=z; Cost[tot]=d; From[tot]=x; } void add_edge(int x,int y,int z,int d) { add(x,y,z,d); add(y,x,0,-d); } bool spfa() { memset(visit,0,sizeof(visit)); memset(Prev,0,sizeof(Prev)); for (int i=1;i<=T;i++) dis[i]=1<<29; int t=0,w=1; Queue[1]=S;visit[S]=1; dis[S]=0; while (t!=w) { t++; if (t>T*2) t=1; int u=Queue[t]; if (u==T) continue; visit[u]=0; for (int i=head[u];i;i=Next[i]) if (val[i]>0) { int v=tree[i]; if (dis[v]>dis[u]+Cost[i]) { dis[v]=dis[u]+Cost[i]; Prev[v]=i; if (!visit[v]) { w++; if (w>T*2) w=1; Queue[w]=v; visit[v]=1; } } } } return Prev[T]!=0; } int GetAns() { int Flow=1<<29,ans=0; for (int i=T;Prev[i];i=From[Prev[i]]) Flow=min(val[Prev[i]],Flow); FLOW+=Flow; for (int i=T;Prev[i];i=From[Prev[i]]) { ans+=Cost[Prev[i]]*Flow; val[Prev[i]]-=Flow; val[Prev[i]^1]+=Flow; } return ans; } int mcf() { int ans=0;FLOW=0;//ans为费用，FLOW为流量。 while (spfa()) ans+=GetAns(); return ans; } } |
