hdu 3416

 先是最小费用流写~~超时,看了看别人的~~

两次最短路,把最短路上的边加入网络流图。再运行最大流。求最小割~~

#include <cstring>
#include <cstdio>
#include <queue>
#define MAXN 2000
#define MAXM 200000
#define inf 0x3f3f3f3f
using namespace std;
struct node
{
    int u,v,f;
};
node e[MAXM*3];
int first[MAXN],next[MAXM*3];
int gap[MAXN],d[MAXN],curedge[MAXN],pre[MAXN];
int cc,inq[MAXN];
int d1[MAXN],d2[MAXN];
int first1[MAXN],first2[MAXN];
int next1[MAXM],next2[MAXM];
struct node1
{
    int u,v;
    int w;
};
node1 e1[MAXM],e2[MAXM];
void spfa(int s,int t)
{
    memset(inq,0,sizeof(inq));
    memset(d1,inf,sizeof(d1));
    memset(d2,inf,sizeof(d2));
    queue<int> q;
    q.push(s);
    d1[s]=0;
    while(!q.empty())
    {
        int u=q.front();
        q.pop();
        inq[u]=0;
        int i;
        for(i=first1[u];i!=-1;i=next1[i])
        {
            int v=e1[i].v;
            if(d1[v]>d1[u]+e1[i].w)
            {
                d1[v]=d1[u]+e1[i].w;
                if(!inq[v])
                {
                    inq[v]=1;
                    q.push(v);
                }
            }
        }
    }
    memset(inq,0,sizeof(inq));
    q.push(t);
    d2[t]=0;
    while(!q.empty())
    {
        int u=q.front();
        q.pop();
        inq[u]=0;
        int i;
        for(i=first2[u];i!=-1;i=next2[i])
        {
            int v=e2[i].v;
            if(d2[v]>d2[u]+e2[i].w)
            {
                d2[v]=d2[u]+e2[i].w;
                if(!inq[v])
                {
                    inq[v]=1;
                    q.push(v);
                }
            }
        }
    }
}
inline void add_edge(int u,int v,int f)
{
    e[cc].u=u;
    e[cc].v=v;
    e[cc].f=f;
    next[cc]=first[u];
    first[u]=cc;
    cc++;

    e[cc].u=v;
    e[cc].v=u;
    e[cc].f=0;
    next[cc]=first[v];
    first[v]=cc;
    cc++;

}
int ISAP(int s,int t,int n)
{
    int cur_flow,flow_ans=0,u,tmp,neck,i,v;
    memset(d,0,sizeof(d));
    memset(gap,0,sizeof(gap));
    memset(pre,-1,sizeof(pre));
    for(i=1;i<=n;i++)
        curedge[i]=first[i];
    gap[0]=n;
    u=s;
    while(d[s]<n)
    {
        if(u==t)
        {
            cur_flow=inf;
            for(i=s;i!=t;i=e[curedge[i]].v)
            {
                if(cur_flow>e[curedge[i]].f)
                {
                    neck=i;
                    cur_flow=e[curedge[i]].f;
                }
            }
            for(i=s;i!=t;i=e[curedge[i]].v)
            {
                tmp=curedge[i];
                e[tmp].f-=cur_flow;
                e[tmp^1].f+=cur_flow;
            }
            flow_ans+=cur_flow;
            u=neck;
        }
        for(i=curedge[u];i!=-1;i=next[i])
        {
            v=e[i].v;
            if(e[i].f&&d[u]==d[v]+1)
                break;
        }
        if(i!=-1)
        {
            curedge[u]=i;
            pre[v]=u;
            u=v;
        }
        else
        {
            if(0==--gap[d[u]])
                break;
            curedge[u]=first[u];
            for(tmp=n+5,i=first[u];i!=-1;i=next[i])
                if(e[i].f)
                    tmp=min(tmp,d[e[i].v]);
            d[u]=tmp+1;
            ++gap[d[u]];
            if(u!=s)
                u=pre[u];
        }
    }
    return flow_ans;
}
int main()
{
    int t;
    scanf("%d",&t);
    while(t--)
    {
        memset(first,-1,sizeof(first));
        memset(next,-1,sizeof(next));
        cc=0;
        int n,m;
        scanf("%d%d",&n,&m);
        int i;
        memset(first1,-1,sizeof(first1));
        memset(first2,-1,sizeof(first2));
        memset(next1,-1,sizeof(next1));
        memset(next2,-1,sizeof(next2));
        for(i=0;i<m;i++)
        {
            int a,b,c;
            scanf("%d%d%d",&a,&b,&c);
            e1[i].u=a;
            e1[i].v=b;
            e1[i].w=c;
            next1[i]=first1[a];
            first1[a]=i;

            e2[i].u=b;
            e2[i].v=a;
            e2[i].w=c;
            next2[i]=first2[b];
            first2[b]=i;

        }
        int s,t;
        scanf("%d%d",&s,&t);
        spfa(s,t);
        for(i=0;i<m;i++)
        {
            int u=e1[i].u;
            int v=e1[i].v;
            if(d1[u]+d2[v]+e1[i].w==d1[t])
            {
                add_edge(u,v,1);
            }
        }
        int res=ISAP(s,t,1000);
        printf("%d\n",res);
    }
    return 0;
}


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