golf

Author: lrvideckis

library/graphs/bridges_cuts/bridges.hpp

@@ -20,18 +20,17 @@
 //! @time O(n + m)
 //! @space O(n + m)
 auto bridges(const auto& adj, int m) {
-  int n = sz(adj), num_ccs = 0, timer = 0;
-  vi br_id(n, -1), is_br(m), tin(n), st;
-  auto dfs = [&](auto&& self, int v, int p_id) -> int {
-    int low = tin[v] = ++timer, siz = sz(st);
-    st.push_back(v);
-    for (auto [u, e_id] : adj[v])
-      if (e_id != p_id && br_id[u] < 0)
-        low = min(low, tin[u] ?: self(self, u, e_id));
+  int n = sz(adj), num_ccs = 0, q = 0, s = 0;
+  vi br_id(n, -1), is_br(m), tin(n), st(n);
+  auto dfs = [&](auto&& self, int v, int p) -> int {
+    int low = tin[v] = ++q;
+    st[s++] = v;
+    for (auto [u, e] : adj[v])
+      if (e != p && br_id[u] < 0)
+        low = min(low, tin[u] ?: self(self, u, e));
     if (tin[v] == low) {
-      if (p_id != -1) is_br[p_id] = 1;
-      rep(i, siz, sz(st)) br_id[st[i]] = num_ccs;
-      st.resize(siz);
+      if (p != -1) is_br[p] = 1;
+      while (br_id[v] < 0) br_id[st[--s]] = num_ccs;
       num_ccs++;
     }
     return low;

library/graphs/bridges_cuts/cuts.hpp

@@ -21,31 +21,29 @@
 //! @time O(n + m)
 //! @space O(n + m)
 auto cuts(const auto& adj, int m) {
-  int n = sz(adj), num_bccs = 0, timer = 0;
-  vi bcc_id(m, -1), is_cut(n), tin(n), st;
-  auto dfs = [&](auto&& self, int v, int p_id) -> int {
-    int low = tin[v] = ++timer, deg = 0;
-    for (auto [u, e_id] : adj[v]) {
+  int n = sz(adj), num_bccs = 0, q = 0, s = 0;
+  vi bcc_id(m, -1), is_cut(n), tin(n), st(m);
+  auto dfs = [&](auto&& self, int v, int p) -> int {
+    int low = tin[v] = ++q, deg = 0;
+    for (auto [u, e] : adj[v]) {
       assert(v != u);
-      if (e_id == p_id) continue;
+      if (e == p) continue;
       if (!tin[u]) {
-        int siz = sz(st);
-        st.push_back(e_id);
-        int low_ch = self(self, u, e_id);
+        st[s++] = e;
+        int low_ch = self(self, u, e);
         if (low_ch >= tin[v]) {
           is_cut[v] = 1;
-          rep(i, siz, sz(st)) bcc_id[st[i]] = num_bccs;
-          st.resize(siz);
+          while (bcc_id[e] < 0) bcc_id[st[--s]] = num_bccs;
           num_bccs++;
         }
         low = min(low, low_ch);
         deg++;
       } else if (tin[u] < tin[v]) {
-        st.push_back(e_id);
+        st[s++] = e;
         low = min(low, tin[u]);
       }
     }
-    if (p_id == -1) is_cut[v] = (deg > 1);
+    if (p == -1) is_cut[v] = (deg > 1);
     return low;
   };
   rep(i, 0, n) if (!tin[i]) dfs(dfs, i, -1);

library/graphs/strongly_connected_components/scc.hpp

@@ -13,17 +13,16 @@
 //! @time O(n + m)
 //! @space O(n)
 auto sccs(const auto& adj) {
-  int n = sz(adj), num_sccs = 0, timer = 0;
-  vi scc_id(n, -1), tin(n), st;
+  int n = sz(adj), num_sccs = 0, q = 0, s = 0;
+  vi scc_id(n, -1), tin(n), st(n);
   auto dfs = [&](auto&& self, int v) -> int {
-    int low = tin[v] = ++timer, siz = sz(st);
-    st.push_back(v);
+    int low = tin[v] = ++q;
+    st[s++] = v;
     for (int u : adj[v])
       if (scc_id[u] < 0)
         low = min(low, tin[u] ?: self(self, u));
     if (tin[v] == low) {
-      rep(i, siz, sz(st)) scc_id[st[i]] = num_sccs;
-      st.resize(siz);
+      while (scc_id[v] < 0) scc_id[st[--s]] = num_sccs;
       num_sccs++;
     }
     return low;