玄学的错误

while(!q.empty())
    {
        u = q.front(), q.pop();
        as = max(as, dp[u]);
        for(int e = hed[u]; e; e = nxt[e])
        {
            v = to[e];
            dp[v] = max(dp[v], dp[u] + (v <= n)); //
            if(!--d[v]) q.push(v);
        }
    }

改成

while(!q.empty())
    {
        u = q.front(), q.pop();
        if(u > n) --dp[u]; //
        as = max(as, dp[u]);
        for(int e = hed[u]; e; e = nxt[e])
        {
            v = to[e];
            dp[v] = max(dp[v], dp[u] + 1); //
            if(!--d[v]) q.push(v);
        }
    }

就 A 了