缩点板子

#include<bits/stdc++.h>
using namespace std;
int n,m;
int a[10010];
vector<int> e[100010],vec[10010];
int idx,cnt,dfn[10010],sccno[10010],low[10010],dp[10010];
long long val[10010];
vector<vector<int> >scc;
stack<int>s;
void dfs(int u){
	dfn[u]=++idx;
    low[u]=dfn[u];
	s.push(u);
	for(auto v:e[u]){
		if(!dfn[v]){
			dfs(v);
			low[u]=min(low[v],dfn[u]);
		}
		else if(!sccno[v]){
			low[u]=min(low[u],dfn[v]);
		}
	}
	if(dfn[u]==low[u]){
        ++cnt;
		while(true){
			int v=s.top();
			s.pop();
			vec[cnt].push_back(v);
			sccno[v]=cnt;
			val[cnt]+=a[v];
			if(v==u)break;
		}
	}
}
int main(){
	cin>>n>>m;
	for(int i=1;i<=n;i++)cin>>a[i];
	for(int i=1;i<=m;i++){
		int u,v;
		cin>>u>>v;
		e[u].push_back(v);
	}
	for(int i=1;i<=n;i++){
		if(!sccno[i])dfs(i);
	}
	int ans=0;
	for(int i=1;i<=cnt;i++){
		dp[i]=val[i];
		for(int u:vec[i]){
			for(int v:e[u]){
				if(sccno[v]==sccno[u])continue;
				else dp[i]=max(dp[i],(int)(dp[sccno[v]]+val[i]));
			}
		}
		ans=max(ans,dp[i]);
	}
    cout<<ans;
	return 0;
}