透彻tarjan

#include<cstdio>
#include<iostream>
#include<cstdlib>
#define N 1000000
#include<vector>
vector <int> scc;
int sta[N],dfn[N],low[N],in[N],tar[N],tot,tp,cnt;
void tarjan(int x)
{
	dfn[x]=low[x]=++tot;
	sta[++tp]=x;
	in[x]=1;
	for(int i=head[x];i;i=e[i].nxt)
	{
		if(!dfn[e[i].to])
		{
			tarjan(e[i].to);
			low[x]=min(low[x],low[e[i].to]);
		}
		else if(in[e[i].to])
		{
			low[x]=min(low[x],dfn[e[i].to]);
		}
	}
	if(dfn[x]==low[x])
	{
		int y;
		cnt++;
		do{
			y=sta[tp--];
			in[y]=0;
			tar[y]=cnt;
			scc[cnt].push_back(y);
		}while(x!=y);
	}
}

#include<cstdio>
#include<iostream>
#include<cstdlib>
#include<queue>
#define N 100000
using namespace std;
int in[N],dfn[N],low[N],sta[N],tot,tp,cnt,nmb,head[N],nmb2;
int n,m,p[N],h[N],tar[N],inn[N],dist[N];
struct node{
	int to,nxt,from;
}e[N<<1],e2[N<<1];
void add(int from,int to)
{
	e[++nmb]= (node) {to,head[from],from};
	head[from]=nmb;
}
void add2(int from,int to)
{
	e2[++nmb2]= (node) {to,h[from],from};
	h[from]=nmb2;
}
void tarjan(int x)
{
	dfn[x]=low[x]=++tot;
	sta[++tp]=x;
	in[x]=1;
	for(int i=head[x];i;i=e[i].nxt)
	{
		int v=e[i].to;
		if(!dfn[v])
		{
			tarjan(v);
			low[x]=min(low[x],low[v]);
		}
		else if(in[v])
		{
			low[x]=min(low[x],dfn[v]);
		}
	}
	if(dfn[x]==low[x])
	{
		int y;
		while(y=sta[tp--])
		{	
			tar[y]=x;
			in[y]=0;
			if(x==y)break;
			p[x]+=p[y];
		}
	}
}
int topo()
{
	queue <int> q;
	for(int i=1;i<=n;i++)
	if(tar[i]==i&&!inn[i])
	{
		q.push(i);
		dist[i]=p[i];
	}
	while(q.size())
	{
		int x=q.front();
		q.pop();
		for(int i=h[x];i;i=e2[i].nxt)
		{
			int y=e2[i].to;
			dist[y]=max(dist[x]+p[y],dist[y]);
			inn[y]--;
			if(inn[y]==0)q.push(y);
		}
	}
	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,x,y;i<=m;i++)
	{
		scanf("%d%d",&x,&y);
		add(x,y);
	}
	for(int i=1;i<=n;i++) if(!dfn[i])tarjan(i);
	for(int i=1;i<=m;i++)
	{
		int x=tar[e[i].from] , y=tar[e[i].to];
		if(x!=y)
		{
			add2(x,y);
			inn[y]++;
		}
	}
	printf("%d\n",topo());
	return 0;
}