tarjan/tarjan-cut.cc

@@ -0,0 +1,20 @@
+void tarjan(int u, int father) {
+  vis[u] = true;
+  low[u] = dfn[u] = ++cnt;
+  int child = 0;
+  for (auto v : edge[u]) { 
+    if (!vis[v]) {
+      child++;
+      tarjan(v, u);
+      low[u] = min(low[u], low[v]);
+      if (father != u && low[v] >= dfn[u] && !flag[u]) {
+        flag[u] = true;
+        res++;
+      }
+    } else if (v != father) low[u] = min(low[u], dfn[v]);
+  }
+  if (father == u && child >= 2 && !flag[u]) {
+    flag[u] = true;
+    res++;
+  }
+}

tarjan/tarjan-scc.cc

@@ -0,0 +1,19 @@
+// st = stack, vis = visited, br = branch(result)
+
+constexpr int MAXN=1e5+10;
+int dfn[MAXN],low[MAXN],st[MAXN],vis[MAXN],br[MAXN];
+int n,cnt,stn,scn;
+vector<int>ch[MAXN];
+void tarjan(int v){
+    dfn[v]=low[v]=++cnt;
+    st[stn++]=v;
+    vis[v]=1;
+    for(const auto&u:ch[v])
+        if(!dfn[u])tarjan(u),low[v]=min(low[v],low[u]);
+        else if(vis[u])low[v]=min(low[v],dfn[u]);
+    if(dfn[v]==low[v]){
+        ++scn;
+        int u;
+        do u=st[--stn],vis[u]=0,br[u]=scn; while(u!=v);
+    }
+}