rename existing class as preorder_tree_dfs

Author: hitonanode

tree/eulertour.hpp

@@ -0,0 +1,30 @@
+#pragma once
+#include <cassert>
+#include <vector>
+
+// Preorder tree DFS
+// 木を DFS して行きがけ順に頂点を保持する．
+// 木を区間に変換する．部分木を構成する頂点は連続して現れるので，部分木の頂点クエリ等に有用．
+// heavy_light_decomposition が上位互換
+struct preorder_tree_dfs {
+    int n; // # of vertices of tree
+    int root;
+    std::vector<int> subtree_begin, subtree_end;
+    std::vector<int> vis_order;
+
+    void _build_dfs(int now, const std::vector<std::vector<int>> &to) {
+        subtree_begin[now] = vis_order.size();
+        vis_order.push_back(now);
+        for (auto nxt : to[now]) {
+            if (subtree_begin[nxt] == -1) _build_dfs(nxt, to);
+        }
+        subtree_end[now] = vis_order.size();
+    }
+
+    preorder_tree_dfs() = default;
+
+    preorder_tree_dfs(const std::vector<std::vector<int>> &to, int root)
+        : n(to.size()), root(root), subtree_begin(n, -1), subtree_end(n, -1) {
+        _build_dfs(root, to);
+    }
+};

tree/preorder_tree_dfs.hpp

@@ -0,0 +1,22 @@
+---
+title: Preorder tree DFS （木の行きがけ順 DFS）
+documentation_of: ./preorder_tree_dfs.hpp
+---
+
+与えられた木に対して，行きがけ順に頂点を列挙した列を構築する．部分木を構成する頂点は連続して現れるので，部分木の頂点クエリ等に有用．
+
+## 使用方法
+
+```cpp
+int N;
+vector<vector<int>> to(N);
+int root;
+
+preorder_tree_dfs tour(to, root);
+
+// 頂点 v の部分木を構成する頂点は半開区間 [tour.subtree_begin[v], tour.subtree_end[v]) に現れる
+```
+
+## 問題例
+
+- [Library Checker: Vertex Add Subtree Sum](https://judge.yosupo.jp/problem/vertex_add_subtree_sum)

tree/preorder_tree_dfs.md

@@ -0,0 +1,39 @@
+#define PROBLEM "https://judge.yosupo.jp/problem/vertex_add_subtree_sum"
+#include "../preorder_tree_dfs.hpp"
+#include <cassert>
+#include <iostream>
+#include <atcoder/fenwicktree>
+using namespace std;
+
+int main() {
+    int N, Q;
+    cin >> N >> Q;
+    vector<long long> A(N);
+    vector<vector<int>> to(N);
+    for (auto &a : A) cin >> a;
+    for (int i = 1; i < N; i++) {
+        int p;
+        cin >> p;
+        to.at(p).push_back(i);
+        to.at(i).push_back(p);
+    }
+
+    preorder_tree_dfs tour(to, 0);
+
+    atcoder::fenwick_tree<long long> ft(N);
+    for (int i = 0; i < N; i++) ft.add(tour.subtree_begin.at(i), A.at(i));
+
+    while (Q--) {
+        int q;
+        cin >> q;
+        if (q) {
+            int u;
+            cin >> u;
+            printf("%lld\n", ft.sum(tour.subtree_begin[u], tour.subtree_end[u]));
+        } else {
+            int u, x;
+            cin >> u >> x;
+            ft.add(tour.subtree_begin[u], x);
+        }
+    }
+}

tree/test/preorder_tree_dfs.test.cpp

@@ -1,41 +1,42 @@
-#include "../../segmenttree/point-update-range-get_nonrecursive.hpp"
-#include "../eulertour.hpp"
 #define PROBLEM "https://judge.yosupo.jp/problem/vertex_add_subtree_sum"
+#include "../heavy_light_decomposition.hpp"
 #include <cassert>
 #include <iostream>
+#include <atcoder/fenwicktree>
 using namespace std;
 
 int main() {
     int N, Q;
     cin >> N >> Q;
     vector<long long> A(N);
-    vector<vector<int>> to(N);
+    vector<pair<int, int>> edges;
     for (auto &a : A) cin >> a;
     for (int i = 1; i < N; i++) {
         int p;
         cin >> p;
-        to[p].push_back(i);
-        to[i].push_back(p);
+        edges.emplace_back(p, i);
     }
 
-    PreorderEulerTour tour(to, 0);
+    heavy_light_decomposition tour(N, edges);
+    tour.build();
+
     vector<long long> v;
     for (auto i : tour.vis_order) v.push_back(A[i]);
     assert(int(v.size()) == N);
-    PointUpdateRangeSum<long long> rsq(v, 0);
+    atcoder::fenwick_tree<long long> ft(N);
+    for (int i = 0; i < N; i++) ft.add(i, v[i]);
 
     while (Q--) {
         int q;
         cin >> q;
         if (q) {
             int u;
             cin >> u;
-            printf("%lld\n", rsq.get(tour.subtree_begin[u], tour.subtree_end[u]));
+            printf("%lld\n", ft.sum(tour.subtree_begin[u], tour.subtree_end[u]));
         } else {
             int u, x;
             cin >> u >> x;
-            A[u] += x;
-            rsq.update(tour.subtree_begin[u], A[u]);
+            ft.add(tour.subtree_begin[u], x);
         }
     }
 }