rerooting: refactoring

tree/rerooting.hpp

@@ -15,67 +15,72 @@ struct rerooting {
     int n_;
     std::vector<int> par, visited;
     std::vector<std::vector<std::pair<int, Edge>>> to;
+
+    // dp_subtree[i] = DP(root=i, edge (i, par[i]) is removed).
     std::vector<Subtree> dp_subtree;
+
+    // dp_par[i] = DP(root=par[i], edge (i, par[i]) is removed). dp_par[root] is meaningless.
     std::vector<Subtree> dp_par;
+
+    // dpall[i] = DP(root=i, all edges exist).
     std::vector<Subtree> dpall;
+
     rerooting(const std::vector<std::vector<std::pair<int, Edge>>> &to_)
         : n_(to_.size()), par(n_, -1), visited(n_, 0), to(to_) {
         for (int i = 0; i < n_; ++i) dp_subtree.push_back(add_vertex(e(), i));
         dp_par = dpall = dp_subtree;
     }
 
     void run_connected(int root) {
-        if (visited[root]) return;
-        visited[root] = 1;
+        if (visited.at(root)) return;
+        visited.at(root) = 1;
         std::vector<int> visorder{root};
 
         for (int t = 0; t < int(visorder.size()); ++t) {
-            int now = visorder[t];
-            for (const auto &edge : to[now]) {
-                int nxt = edge.first;
-                if (visited[nxt]) continue;
+            int now = visorder.at(t);
+            for (const auto &[nxt, _] : to[now]) {
+                if (visited.at(nxt)) continue;
                 visorder.push_back(nxt);
-                visited[nxt] = 1;
-                par[nxt] = now;
+                visited.at(nxt) = 1;
+                par.at(nxt) = now;
             }
         }
 
         for (int t = int(visorder.size()) - 1; t >= 0; --t) {
-            int now = visorder[t];
+            const int now = visorder.at(t);
             Children ch = e();
-            for (const auto &edge : to[now]) {
-                int nxt = edge.first;
-                if (nxt == par[now]) continue;
-                ch = rake(ch, add_edge(dp_subtree[nxt], nxt, edge.second));
+            for (const auto &[nxt, edge] : to.at(now)) {
+                if (nxt != par.at(now)) ch = rake(ch, add_edge(dp_subtree.at(nxt), nxt, edge));
             }
-            dp_subtree[now] = add_vertex(ch, now);
+            dp_subtree.at(now) = add_vertex(ch, now);
         }
 
         std::vector<Children> left;
         for (int now : visorder) {
-            int m = int(to[now].size());
+            const int m = to.at(now).size();
             left.assign(m + 1, e());
             for (int j = 0; j < m; j++) {
-                int nxt = to[now][j].first;
-                const Subtree &st = (nxt == par[now] ? dp_par[now] : dp_subtree[nxt]);
-                left[j + 1] = rake(left[j], add_edge(st, nxt, to[now][j].second));
+                const auto &[nxt, edge] = to.at(now).at(j);
+                const Subtree &st = (nxt == par.at(now) ? dp_par.at(now) : dp_subtree.at(nxt));
+                left.at(j + 1) = rake(left.at(j), add_edge(st, nxt, edge));
             }
-            dpall[now] = add_vertex(left.back(), now);
+            dpall.at(now) = add_vertex(left.back(), now);
 
             Children rprod = e();
             for (int j = m - 1; j >= 0; --j) {
-                int nxt = to[now][j].first;
-                if (nxt != par[now]) dp_par[nxt] = add_vertex(rake(left[j], rprod), now);
+                const auto &[nxt, edge] = to.at(now).at(j);
+
+                if (nxt != par.at(now)) dp_par.at(nxt) = add_vertex(rake(left.at(j), rprod), now);
 
-                const Subtree &st = (nxt == par[now] ? dp_par[now] : dp_subtree[nxt]);
-                rprod = rake(add_edge(st, nxt, to[now][j].second), rprod);
+                const Subtree &st = (nxt == par.at(now) ? dp_par.at(now) : dp_subtree.at(nxt));
+                rprod = rake(add_edge(st, nxt, edge), rprod);
             }
         }
     }
 
     void run() {
         for (int i = 0; i < n_; ++i) {
-            if (!visited[i]) run_connected(i);
+            if (!visited.at(i)) run_connected(i);
         }
     }