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Codeforces Round 1037 (Div. 3)/F. 1-1-1, Free Tree!.cpp

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+/* Problem URL: https://codeforces.com/problemset/problem/2126/F */
+
+#include <bits/stdc++.h>
+#include <ext/pb_ds/assoc_container.hpp>
+#include <ext/pb_ds/tree_policy.hpp>
+
+using namespace std;
+using namespace __gnu_pbds;
+
+template <class T, class comp = less<>>
+using ordered_set = tree<T, null_type , comp , rb_tree_tag , tree_order_statistics_node_update>;
+
+#define V vector
+
+#define rmin(a, b) a = min(a, b)
+#define rmax(a, b) a = max(a, b)
+
+#define rep(i, lim) for (int i = 0; i < (lim); i++)
+#define nrep(i, s, lim) for (int i = s; i < (lim); i++)
+
+#define repv(i, v) for (auto &i : (v))
+#define fillv(v) for (auto &itr_ : (v)) { cin >> itr_; }
+#define sortv(v) sort(v.begin(), v.end())
+#define all(v) (v).begin(), (v).end()
+
+using vi = vector<int>;
+using vvi = vector<vi>;
+using vvvi = vector<vvi>;
+using vvvvi = vector<vvvi>;
+
+using ll = long long;
+
+using vl = vector<ll>;
+using vvl = vector<vl>;
+using vvvl = vector<vvl>;
+using vvvvl = vector<vvvl>;
+
+template<class v>
+auto operator<<(ostream &os, const vector<v> &vec)->ostream& {
+    os << vec[0];
+    for (size_t i = 1; i < vec.size(); i++) {
+        os << ' ' << vec[i];
+    }
+    os << '\n';
+    return os;
+}
+
+template<class v>
+auto operator>>(istream &is, vector<v> &vec)->istream& {
+    for (auto &i : vec) {
+        is >> i;
+    }
+    return is;
+}
+
+template<class v>
+auto operator<<(ostream &os, const vector<vector<v>> &vec)->ostream& {
+    for (auto &i : vec) {
+        os << i[0];
+        for (size_t j = 1; j < i.size(); j++) {
+            os << ' ' << i[j];
+        }
+        os << '\n';
+    }
+    return os;
+}
+
+template<class v>
+auto operator>>(istream  &is, vector<vector<v>> &vec)->istream& {
+    for (auto &i : vec) {
+        for (auto &j : i) {
+            is >> j;
+        }
+    }
+    return is;
+}
+
+int main()
+{
+    ios::sync_with_stdio(false);
+    cin.tie(nullptr);
+
+    int t;
+    cin >> t;
+    while (t--) {
+        int n, q;
+        cin >> n >> q;
+
+        vi fds(n);
+        cin >> fds;
+
+        V<unordered_map<int, ll>> cl(n);
+        V<V<pair<int, ll>>> graph(n);
+        vi par(n);
+        vl cost(n);
+
+        rep(i, n - 1) {
+            int a, b;
+            ll c;
+            cin >> a >> b >> c;
+            a--, b--;
+
+            graph[a].emplace_back(b, c);
+            graph[b].emplace_back(a, c);
+        }
+
+        ll ans = 0;
+
+        function<void(int, int)> dfs = [&](int i, int p) {
+            for (auto [j, c] : graph[i]) {
+                if (j == p) {
+                    continue;
+                }
+
+                if (fds[j] != fds[i]) {
+                    ans += c;
+                }
+
+                cl[i][fds[j]] += c;
+                par[j] = i;
+                cost[j] = c;
+
+                dfs(j, i);
+            }
+        };
+
+        dfs(0, 0);
+
+        while (q--) {
+            int a, c;
+            cin >> a >> c;
+            a--;
+
+            ans += cl[a][fds[a]];
+            ans -= cl[a][c];
+
+            if (a != 0) {
+                cl[par[a]][fds[a]] -= cost[a];
+                cl[par[a]][c] += cost[a];
+
+                if (c != fds[par[a]] && fds[a] == fds[par[a]]) {
+                    ans += cost[a];
+                } else if (c == fds[par[a]] && fds[a] != fds[par[a]]) {
+                    ans -= cost[a];
+                }
+            }
+
+            fds[a] = c;
+
+            cout << ans << '\n';
+        }
+    }
+}