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和poj3592一个套路 缩完点跑最长路 但是要注意 缩点时不能把负值加上!

#include <cstdio>
#include <queue>
#include <stack>
#include <cstring>
#include <algorithm>
using namespace std;
#define N 0x3f3f3f3f

struct node
{
    int v;
    int w;
    int next;
};

stack <int> stk;
queue <int> que;
node edge1[150010],edge2[150010];
int per[30010],dis[30010],first1[30010],first2[30010],dfn[30010],low[30010],book[30010],belong[30010],val[30010],degree[30010];
int n,m,num,tot;

void addedge(node* edge,int* first,int u,int v,int w)
{
    edge[num].v=v;
    edge[num].w=w;
    edge[num].next=first[u];
    first[u]=num++;
    return;
}

void dfs(int cur)
{
    int i,v;
    stk.push(cur);
    num++;
    dfn[cur]=num,low[cur]=num,book[cur]=1;
    for(i=first1[cur];i!=-1;i=edge1[i].next)
    {
        v=edge1[i].v;
        if(!dfn[v])
        {
            dfs(v);
            low[cur]=min(low[cur],low[v]);
        }
        else if(book[v])
        {
            low[cur]=min(low[cur],dfn[v]);
        }
    }
    if(dfn[cur]==low[cur])
    {
        tot++;
        while(!stk.empty())
        {
            v=stk.top();
            stk.pop();
            book[v]=0;
            belong[v]=tot;
            if(per[v]>=0) val[tot]+=per[v];
            if(cur==v) break;
        }
    }
    return;
}

void tarjan()
{
    int i,u,v;
    while(!stk.empty()) stk.pop();
    memset(dfn,0,sizeof(dfn));
    memset(low,0,sizeof(low));
    memset(book,0,sizeof(book));
    memset(belong,0,sizeof(belong));
    memset(val,0,sizeof(val));
    num=0,tot=0;
    for(i=1;i<=n;i++)
    {
        if(!dfn[i]) dfs(i);
    }
    memset(first2,-1,sizeof(first2));
    memset(degree,0,sizeof(degree));
    num=0;
    for(u=1;u<=n;u++)
    {
        for(i=first1[u];i!=-1;i=edge1[i].next)
        {
            v=edge1[i].v;
            if(belong[u]!=belong[v])
            {
                addedge(edge2,first2,belong[u],belong[v],val[belong[v]]);
                degree[belong[v]]++;
            }
        }
    }
    return;
}

int spfa()
{
    int i,u,v,w,maxx;
    while(!que.empty()) que.pop();
    for(i=1;i<=tot;i++)
    {
        dis[i]=-N;
        book[i]=0;
    }
    for(i=1;i<=tot;i++)
    {
        if(!degree[i])
        {
            que.push(i);
            dis[i]=val[i];
            book[i]=1;
        }
    }
    while(!que.empty())
    {
        u=que.front();
        que.pop();
        book[u]=0;
        for(i=first2[u];i!=-1;i=edge2[i].next)
        {
            v=edge2[i].v,w=edge2[i].w;
            if(dis[v]<dis[u]+w)
            {
                dis[v]=dis[u]+w;
                if(!book[v])
                {
                    que.push(v);
                    book[v]=1;
                }
            }
        }
    }
    maxx=0;
    for(i=1;i<=tot;i++)
    {
        maxx=max(maxx,dis[i]);
    }
    return maxx;
}

int main()
{
    int i,u,v;
    while(scanf("%d%d",&n,&m)!=EOF)
    {
        for(i=1;i<=n;i++)
        {
            scanf("%d",&per[i]);
        }
        memset(first1,-1,sizeof(first1));
        num=0;
        for(i=1;i<=m;i++)
        {
            scanf("%d%d",&u,&v);
            u++,v++;
            addedge(edge1,first1,u,v,0);
        }
        tarjan();
        printf("%d\n",max(0,spfa()));
    }
    return 0;
}