QWQ谢谢

#include <cstdio>
#include <cstring>
#include <algorithm>
#include <iostream>
#include <stack>
using namespace std;
typedef long long ll;
const ll MAXN=1e5+5;
struct edge{
    ll from,to,nxt;
}e[MAXN],e1[MAXN];
ll head[MAXN],tot;
void add(ll u,ll v,edge E[]){
    E[++tot].nxt=head[u];
    head[u]=tot;
    E[tot].from=u;
    E[tot].to=v;
}
ll pre[MAXN],low[MAXN],dt,sccNo[MAXN],sccCount,value[MAXN],a[MAXN];
stack<ll>s;
void tarjan(ll u){
    pre[u]=low[u]=++dt;
    s.push(u);
    for (ll i = head[u]; i ; i=e[head[u]].nxt) {
        ll v=e[i].to;
        if(pre[v]==0){
            tarjan(v);
            low[u]= min(low[u],low[v]);
        }else if(sccNo[v]==0){
            low[u]= min(low[u],pre[v]);
        }
    }
    if(pre[u]==low[u]){
        sccCount++;
        while (true){
            ll t=s.top();
            s.pop();
            sccNo[t]=sccCount;
            value[sccCount]+=a[t];
            if(t==u){
                break;
            }
        }
    }
}
ll f[MAXN];
void dfs(ll u){
    if(f[u]){
        return;
    }
    f[u]=value[u];
    ll Max=0;
    for (int i = head[u]; i ; i=e1[head[u]].nxt) {
        dfs(e1[i].to);
        Max= max(Max,f[e[i].to]);
    }
    f[u]+=Max;
}
ll n,m;
int main(){
    scanf("%lld%lld",&n,&m);
    for (int i = 1; i <=n ; ++i) {
        scanf("%lld",&a[i]);
    }
    for (int i = 1; i <=m ; ++i) {
        ll u,v;
        scanf("%lld%lld",&u,&v);
        add(u,v,e);
    }
    for (int i = 1; i <=n ; ++i) {
        if(pre[i]==0){
            tarjan(i);
        }
    }
    memset(head,0,sizeof(head));
    tot=0;
    for (int i = 1; i <=m ; ++i) {
        if(sccNo[e[i].to]!=sccNo[e[i].from]){
            add(sccNo[e[i].from],sccNo[e[i].to],e1);
        }
    }
    ll ans=0;
    for (int i = 1; i <=sccCount ; ++i) {
        if(!f[i]){
            dfs(i);
            ans= max(ans,f[i]);
        }
    }
    printf("%lld\n",ans);
    return 0;
}