要跑最长路  记搜超时

/**************************************************************    Problem: 1179    User: lxy8584099    Language: C++    Result: Accepted    Time:7020 ms    Memory:58476 kb****************************************************************/ /*    缩点后dfs 途中更新答案 */#include
     
      #include
      
       #include
       
        using namespace std;const int N=500050;struct pp {
   int u,v,nxt;} e[N]; int head[N],tot,n,m,o,a[N],st,maxn;int sta[N],dfn[N],low[N],top,fa[N],dis[N];bool vis[N],bar[N];void add(int u,int v){    e[++tot].nxt=head[u],head[u]=tot;    e[tot].v=v;e[tot].u=u;}int min(int a,int b) {
   return a>b?b:a;} int max(int a,int b) {
   return a>b?a:b;} void tarjan(int u){    vis[u]=1;sta[++top]=u;    dfn[u]=low[u]=++tot;    for(int j=head[u];j;j=e[j].nxt)    {        int v=e[j].v;        if(!dfn[v])        {            tarjan(v);low[u]=min(low[u],low[v]);        }        else if(vis[v]) low[u]=min(low[u],dfn[v]);    }    if(low[u]==dfn[u])    {//      printf("______________________________________\n");        int x;        do        {            x=sta[top--];vis[x]=0;fa[x]=u;bar[u]|=bar[x];//          printf("%d\n",x);            if(x!=u) a[u]+=a[x];        }while(x!=u);    }}void spfa(){    queue
        
          q;q.push(st); dis[st]=a[st];    while(!q.empty())    {        int u=q.front(); q.pop();        vis[u]=0;        for(int j=head[u];j;j=e[j].nxt)        {            int v=e[j].v;            if(dis[v]