最大网络最小流

const int maxn=805;const int maxm=2000005;int first[maxn],dis[maxn],vis[maxn],pre[maxn];int u[maxm],v[maxm],w[maxm],cost[maxm],flow[maxm],nex[maxm];int n,m,vcnt,ecnt,vcnt1,vcnt2;void add_(int a,int b,int c,int d){    u[ecnt]=a;    v[ecnt]=b;    w[ecnt]=c;    cost[ecnt]=d;    flow[ecnt]=0;    nex[ecnt]=first[a];    first[a]=ecnt++;    u[ecnt]=b;    v[ecnt]=a;    w[ecnt]=0;    cost[ecnt]=-d;    flow[ecnt]=0;    nex[ecnt]=first[b];    first[b]=ecnt++;    //cout<<"----"<<a<<" "<<b<<c<<d<<endl;}bool Spfa(int s,int t){    queue<int>q;    memset(dis,0x3f,sizeof dis);    memset(vis,0,sizeof vis);    memset(pre,-1,sizeof pre);    dis[s]=0;    vis[s]=1;    q.push(s);    while(!q.empty())    {        int x=q.front();q.pop();        vis[x]=0;        for(int e=first[x];~e;e=nex[e])        if(w[e]>flow[e]&&dis[v[e]]>dis[x]+cost[e])        {            dis[v[e]]=dis[x]+cost[e];            pre[v[e]]=e;            if(!vis[v[e]])            {                vis[v[e]]=1;                q.push(v[e]);            }        }    }    if(pre[t]==-1)return false;    return true;}int mcmf(int s,int t,int &co){    int flo=0;    co=0;    while(Spfa(s,t))    {        int mmin=inf;        for(int i=pre[t];~i;i=pre[v[i^1]])        {            mmin=min(mmin,w[i]-flow[i]);        }        for(int i=pre[t];~i;i=pre[v[i^1]])        {            flow[i]+=mmin;            flow[i^1]-=mmin;            co+=cost[i]*mmin;        }        flo+=mmin;    }    return flo;}