Tarjan缩点

#include<iostream>
#include<vector>
#include<queue>
#define il inline
#define ri register int
using namespace std;
const int maxn=1e4+2,maxm=1e5;
int val[maxn],sval[maxn],head[maxn],n,m,tot,timeclocks,indeg[maxn],f[maxn];
int dfn[maxn],low[maxn],_stack[maxn],top,cnt,col,belong[maxn],ne[maxn],ans=-1;
bool instack[maxn];
vector<int> in[maxn],out[maxn];
struct Node{int frm,to,nxt;}edge[maxm];
il void add(int u,int v)
{
	edge[++tot].to=v,edge[tot].frm=u,
	edge[tot].nxt=head[u],head[u]=tot;
}
il void init()
{
	ios::sync_with_stdio(false);
	cin>>n>>m;
	for(ri i=1;i<=n;++i) cin>>val[i];
	for(ri i=1,u,v;i<=m;++i) cin>>u>>v,add(u,v);	
}
il void topo()
{
	queue<int> q;
	for(ri i=1;i<=col;++i) if(!indeg[i]) q.push(i);
	while(!q.empty())
	{
		int u=q.front();q.pop();ne[++cnt]=u;	
		for(ri i=0;i<out[u].size();++i)
		{
			--indeg[out[u][i]];
			if(!indeg[out[u][i]]) q.push(out[u][i]);
		}
	}
}
il void Tarjan(int u)
{
	low[u]=dfn[u]=++timeclocks,
	_stack[++top]=u,instack[u]=true;
	for(ri i=head[u];i;i=edge[i].nxt)
	{
		int t=edge[i].to;
		if(!dfn[t]) Tarjan(t),low[u]=min(low[u],low[t]);
		else if(instack[t]) low[u]=min(low[u],dfn[t]);
	}
	if(low[u]==dfn[u])
	{
		++col;
		while(_stack[top+1]!=u)
			sval[col]+=val[_stack[top]],
			instack[_stack[top]]=false,belong[_stack[top--]]=col;
	}
}
il void solve()
{
	for(ri i=1;i<=n;++i)
		if(!dfn[i]) Tarjan(i);
}
il void build()
{
	for(ri i=1;i<=tot;++i)
		if(belong[edge[i].frm]!=belong[edge[i].to])
		{
			int nfm=belong[edge[i].frm],nto=belong[edge[i].to];
			++indeg[nto],out[nfm].push_back(nto),in[nto].push_back(nfm);
		}
}
il void dp()
{
	for(ri i=1;i<=col;++i)
	{
		int u=ne[i];f[u]=sval[u];
		for(ri j=0;j<in[u].size();++j)
			f[u]=max(f[u],f[in[u][j]]+sval[u]);
	}
	for(ri i=1;i<=col;++i) ans=max(ans,f[i]);
	cout<<ans;
}
int main()
{
	init();
	solve();
	build();
	topo();
	dp();
	return 0;
 }