【模板】缩点

题面

tarjan 缩点加dp

#include<bits/stdc++.h>
using namespace std;

const int maxn=10000+15;
int n,m,sum,tim,top,s;
int p[maxn],head[maxn],sd[maxn],dfn[maxn],low[maxn];//DFN(u)为节点u搜索被搜索到时的次序编号(时间戳)，Low(u)为u或u的子树能够追溯到的最早的栈中节点的次序号 
int stac[maxn],vis[maxn];//栈只为了表示此时是否有父子关系 
int h[maxn],in[maxn],dist[maxn];
struct EDGE
{
    int to;int next;int from;
}edge[maxn*10],ed[maxn*10];
void add(int x,int y)
{
    edge[++sum].next=head[x];
    edge[sum].from=x;
    edge[sum].to=y;
    head[x]=sum;
}
void tarjan(int x)
{
    low[x]=dfn[x]=++tim;
    stac[++top]=x;vis[x]=1;
    for (int i=head[x];i;i=edge[i].next)
    {
        int v=edge[i].to;
        if (!dfn[v]) {
        tarjan(v);
        low[x]=min(low[x],low[v]);
    }
        else if (vis[v])
        {
            low[x]=min(low[x],low[v]);
        }
    }
    if (dfn[x]==low[x])
    {
        int y;
        while (y=stac[top--])
        {
            sd[y]=x;
            vis[y]=0;
            if (x==y) break;
            p[x]+=p[y];
        }
    }
}
int topo()
{
    queue <int> q;
    int tot=0;
    for (int i=1;i<=n;i++)
    if (sd[i]==i&&!in[i])
    {
        q.push(i);
        dist[i]=p[i];
     } 
    while (!q.empty())
    {
        int k=q.front();q.pop();
        for (int i=h[k];i;i=ed[i].next)
        {
            int v=ed[i].to;
            dist[v]=max(dist[v],dist[k]+p[v]);
            in[v]--;
            if (in[v]==0) q.push(v);
        }
    }
    int ans=0;
    for (int i=1;i<=n;i++)
    ans=max(ans,dist[i]);
    return ans;
}
int main()
{
    scanf("%d%d",&n,&m);
    for (int i=1;i<=n;i++)
    scanf("%d",&p[i]);
    for (int i=1;i<=m;i++)
    {
        int u,v;
        scanf("%d%d",&u,&v);
        add(u,v);
    }
    for (int i=1;i<=n;i++)
    if (!dfn[i]) tarjan(i);
    for (int i=1;i<=m;i++)
    {
        int x=sd[edge[i].from],y=sd[edge[i].to];
        if (x!=y)
        {
            ed[++s].next=h[x];
            ed[s].to=y;
            ed[s].from=x;
            h[x]=s;
            in[y]++;
        }
    }
    printf("%d",topo());
    return 0;
}