delete pics to save space

1.3387.cpp

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+// luogu-judger-enable-o2
+#include<cstdio>
+#include<vector>
+#include<stack>
+#include<algorithm>
+using namespace std;
+const int maxn=1e4+5;
+int n,m;
+vector<int> G[maxn];
+int dfn[maxn],lowlink[maxn],sccno[maxn],dfs_cnt,scc_cnt;
+int v[maxn],sv[maxn]; vector<int> sg[maxn];
+stack<int> S;
+void dfs(int u)
+{
+	dfn[u]=lowlink[u]=++dfs_cnt;
+	S.push(u);
+	for(int i=0;i<G[u].size();i++)
+	{
+		int v=G[u][i];
+		if(!dfn[v])
+		{
+			dfs(v);
+			lowlink[u]=min(lowlink[u],lowlink[v]);
+		}
+		else if(!sccno[v]) lowlink[u]=min(lowlink[u],dfn[v]);
+	}
+	if(lowlink[u]==dfn[u])
+	{
+		scc_cnt++;
+		while(true)
+		{
+			int x=S.top(); S.pop();
+			sccno[x]=scc_cnt;
+			if(x==u) break;
+		}
+	}
+}
+int f[maxn]; bool vis[maxn];
+int dp(int u)
+{
+	int &res=f[u];
+	if(vis[u]) return res;
+	vis[u]=true;
+	res=sv[u];
+	for(int i=0;i<sg[u].size();i++) res=max(res,sv[u]+dp(sg[u][i]));
+	return res;
+}
+int main()
+{
+#ifdef local
+	freopen("pro.in","r",stdin);
+#endif
+	scanf("%d%d",&n,&m);
+	for(int i=1;i<=n;i++) scanf("%d",&v[i]);
+	for(int i=0;i<m;i++)
+	{
+		int u,v; scanf("%d%d",&u,&v);
+		G[u].push_back(v);
+	}
+	for(int i=1;i<=n;i++) if(!dfn[i]) dfs(i);
+	for(int i=1;i<=n;i++) sv[sccno[i]]+=v[i];
+	for(int u=1;u<=n;u++)
+		for(int i=0;i<G[u].size();i++)
+		{
+			int v=G[u][i];
+			if(sccno[v]!=sccno[u]) sg[sccno[u]].push_back(sccno[v]);
+		}
+	int res=0;
+	for(int i=1;i<=scc_cnt;i++) res=max(res,dp(i));
+	printf("%d\n",res);
+	return 0;
+}