Kosaraju 算法

#include<bits/stdc++.h>
using namespace std;
const int MAXN = 1e5 + 10;
int n,m,a[MAXN],na[MAXN];
bool vis[MAXN];
vector<int>v[MAXN],v2[MAXN];
vector<int>s;
vector<int>nv[MAXN];
void dfs1(int x){
	vis[x]=1;
	for(auto i:v[x]){
		if(!vis[i]) {
			vis[i]=1;
			dfs1(i);
			
		}
	}
	s.push_back(x);
}
int sccs=0,color[MAXN];
void dfs2(int x){
	color[x]=sccs;
	for(auto i:v2[x]){
		if(!color[i]){
			color[i]=sccs;
			dfs2(i);
		}
	}
}
int lg[MAXN];
int dfs3(int x,int last){
	if(lg[x]) return lg[x];
	int e=0;
	for(auto i:nv[x]){
		if(i!=x) e=max(e,dfs3(i,x));
	}
	lg[x]=e+na[x];
	return lg[x];
}
signed main()
{
	ios::sync_with_stdio(0);
	cin.tie(0);cout.tie(0);
	cin>>n>>m;
	for(int i=1;i<=n;i++){
		cin>>a[i];
	}
	for(int i=1;i<=m;i++){
		int x,y;
		cin>>x>>y;
		v[x].push_back(y);
		v2[y].push_back(x);
	}
	for(int i=1;i<=n;i++){
		if(!vis[i]){
			dfs1(i);
		}
	}
	sccs=0;
	for(int i=n;i>0;i--){
		if(!color[i]){
			sccs++;
			dfs2(i);
		}
	}
	for(int i=1;i<=n;i++){
		na[color[i]]+=a[i];
		for(int k:v[i]){
			bool flag=1;
			for(int j=0;j<nv[color[i]].size();j++){
				if(nv[color[i]][j]==k){
					flag=0;
					break;
				}
			}
			if(flag) nv[color[i]].push_back(k);
		}
	}
	memset(vis,0,sizeof(vis));
	int ans=0;
	for(int i=1;i<=sccs;i++){
		if(!lg[i])ans=max(ans,dfs3(i,0));
	}
	cout<<ans;
	return 0;
}