BZOJ 1266 上学路线route（最小割）

struct node
{
    int v,cap,next;
};
 
node edges[N];
int head[N],e;
 
void add(int u,int v,int cap)
{
    edges[e].v=v;
    edges[e].cap=cap;
    edges[e].next=head[u];
    head[u]=e++;
}
 
void Add(int u,int v,int cap)
{
    add(u,v,cap);
    add(v,u,0);
}
 
int pre[N],cur[N],num[N],h[N];
 
int Maxflow(int s,int t,int n)
{
    int i;
    for(i=0;i<=n;i++) cur[i]=head[i],num[i]=h[i]=0;
    int u=s,Min,k,v;
    int ans=0;
    while(h[u]<n)
    {
        if(u==t)
        {
            Min=INF;
            for(i=s;i!=t;i=edges[cur[i]].v)
            {
                k=cur[i];
                if(edges[k].cap<Min) Min=edges[k].cap,v=i;
            }
            ans+=Min; u=v;
            for(i=s;i!=t;i=edges[cur[i]].v)
            {
                k=cur[i];
                edges[k].cap-=Min;
                edges[k^1].cap+=Min;
            }
        }
        for(i=cur[u];i!=-1;i=edges[i].next)
        {
            if(edges[i].cap>0&&h[u]==h[edges[i].v]+1) break;
        }
        if(i!=-1)
        {
            cur[u]=i;
            pre[edges[i].v]=u;
            u=edges[i].v;
        }
        else
        {
            if(--num[h[u]]==0) break;
            k=n;
            cur[u]=head[u];
            for(i=head[u];i!=-1;i=edges[i].next)
            {
                if(edges[i].cap>0&&h[edges[i].v]<k)
                {
                    k=h[edges[i].v];
                }
            }
            num[k+1]++;
            h[u]=k+1;
            if(u!=s) u=pre[u];
        }
    }
    return ans;
}


struct Node
{
    int u,v,w,c,next;
};


Node edge[300000];
int head1[505],e1;


void add1(int u,int v,int w,int c)
{
    edge[e1].u=u;
    edge[e1].v=v;
    edge[e1].w=w;
    edge[e1].c=c;
    edge[e1].next=head1[u];
    head1[u]=e1++;
}


int n,m,dis1[505],dis2[505];
int inq[505];


void BFS(int dis[],int s)
{
    int i;
    FOR1(i,n) dis[i]=INF,inq[i]=0;
    queue<int> Q; 
    Q.push(s);
    dis[s]=0;
    int u,v;
    while(!Q.empty())
    {
        u=Q.front();
        Q.pop();
        
        inq[u]=0;
        
        for(i=head1[u];i!=-1;i=edge[i].next)
        {
            v=edge[i].v;
            if(dis[v]>dis[u]+edge[i].w)
            {
                dis[v]=dis[u]+edge[i].w;
                if(!inq[v]) inq[v]=1,Q.push(v);
            }
        }
    }
}


void build()
{
    clr(head,-1);
    int i,u,v,c;
    FOR0(i,e1)
    {
        u=edge[i].u;
        v=edge[i].v;
        c=edge[i].c;
        if(dis1[u]+edge[i].w+dis2[v]==dis1[n])
        {
            if(u!=n&&v!=1) Add(u,v,c);
        }
    }
}


int main()
{
    RD(n,m); clr(head1,-1);
    int i,u,v,w,c;
    FOR1(i,m)
    {
        RD(u,v); RD(w,c);
        add1(u,v,w,c);
        add1(v,u,w,c);
    }
    BFS(dis1,1);  BFS(dis2,n);
    build(); PR(dis1[n]);
    PR(Maxflow(1,n,n));
}