poj 2987 最大闭合子图

思路：

这题考的是最大闭权图。只要知道怎么求最大闭权图就知道怎么做。但好像有点卡模版，要高效的模版才行。

#include <iostream>

#include <stdio.h>

#include <string.h>

#define Maxn 6010

#define Maxm 200000

#define LL __int64

#define Abs(a) (a)>0?(a):(-a)

using namespace std;

struct Edge{

    int from,to,next;

    LL val;

}edge[Maxm];

LL value[Maxn],inf=0;

int index[Maxn],work[Maxn],dis[Maxn],q[Maxn],e,vi[Maxn];

inline void addedge(int from,int to,LL val)//有向边

{

    edge[e].from=from;

    edge[e].to=to;

    edge[e].val=val;

    edge[e].next=index[from];

    index[from]=e++;

    edge[e].from=to;

    edge[e].to=from;

    edge[e].val=0;

    edge[e].next=index[to];

    index[to]=e++;

}

void init()

{

    e=0;

    memset(index,-1,sizeof(index));

    memset(vi,0,sizeof(vi));

    inf=0;

}

void add(int u,int v,LL c)

{

    edge[e].to=v;edge[e].val=c;edge[e].next=index[u];index[u]=e++;

    edge[e].to=u;edge[e].val=0;edge[e].next=index[v];index[v]=e++;

}

void DFS(int u)

{

    vi[u]=1;

    int i,v;

    for(i=index[u];i!=-1;i=edge[i].next)

        if(edge[i].val&&!vi[edge[i].to])

            DFS(edge[i].to);

}

int bfs(int S,int T)

{

    int rear=0;

    memset(dis,-1,sizeof(dis));

    dis[S]=0;q[rear++]=S;

    for(int i=0;i<rear;i++)

    {

        for(int j=index[q[i]];j!=-1;j=edge[j].next)

        {

            if(edge[j].val&&dis[edge[j].to]==-1)

            {

                dis[edge[j].to]=dis[q[i]]+1;

                q[rear++]=edge[j].to;

                if(edge[j].to==T) return 1;

            }

        }

    }

    return 0;

}

LL dfs(int cur,LL a,int T)

{

    if(cur==T) return a;

    for(int &i=work[cur];i!=-1;i=edge[i].next)

    {

        if(edge[i].val&&dis[edge[i].to]==dis[cur]+1)

        {

            int t=dfs(edge[i].to,min(a,edge[i].val),T);

            if(t)

            {

                edge[i].val-=t;

                edge[i^1].val+=t;

                return t;

            }

        }

    }

    return 0;

}

LL Dinic(int S,int T)

{

    LL ans=0;

    while(bfs(S,T))

    {

        memcpy(work,index,sizeof(index));

        while(int t=dfs(S,inf,T)) ans+=t;

    }

    return ans;

}



int main()

{

    int n,m,i,a,b;

    LL sum=0;

    scanf("%d%d",&n,&m);

    init();

    for(i=1;i<=n;i++)

    {

        scanf("%I64d",value+i);

        if(value[i]>0)

        {

            sum+=value[i];

            addedge(0,i,value[i]);

        }

        else

        addedge(i,n+1,-value[i]);

        inf+=Abs(value[i]);

    }

    inf++;

    for(i=1;i<=m;i++)

    {

        scanf("%d%d",&a,&b);

        addedge(a,b,inf);

    }

    LL ans=Dinic(0,n+1);//起始点和结束点

    //DFS(0);//寻找S集合

    int num=0;

    for(i=1;i<=n;i++)

        if(dis[i]>=0)

            num++;

    printf("%d %I64d\n",num,sum-ans);

    return 0;

}