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Codeforces Round 998 (Div. 3)/E. Graph Composition.cpp

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+/* Problem URL: https://codeforces.com/contest/2060/problem/E */
+
+#include <bits/stdc++.h>
+
+using namespace std;
+
+#define V vector
+
+#define rmin(a, b) a = min(a, b)
+#define rmax(a, b) a = max(a, b)
+
+#define rep(i, lim) for (size_t i = 0; i < (lim); i++)
+#define nrep(i, s, lim) for (size_t 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;
+}
+
+void dothething(int i, V<bool> &vis, vi &groups, int group, vvi &graph)
+{
+    vis[i] = true;
+    groups[i] = group;
+
+    repv(c, graph[i]) {
+        if (vis[c]) {
+            continue;
+        }
+
+        dothething(c, vis, groups, group, graph);
+    }
+}
+
+int get(int i, V<bool> &vis, vi &groups, vvi &graph)
+{
+    vis[i] = true;
+
+    int invalid = 0;
+    repv(c, graph[i]) {
+        if (vis[c]) {
+            continue;
+        }
+
+        if (groups[i] != groups[c]) {
+            invalid++;
+            continue;
+        }
+
+        invalid += get(c, vis, groups, graph);
+    }
+
+    return invalid;
+}
+
+int main()
+{
+    ios::sync_with_stdio(false);
+    cin.tie(nullptr);
+
+    int t;
+    cin >> t;
+    while (t--) {
+        int n, m1, m2;
+        cin >> n >> m1 >> m2;
+
+        vvi f(n);
+        rep(i, m1) {
+            int a, b;
+            cin >> a >> b;
+            a--, b--;
+            f[a].push_back(b);
+            f[b].push_back(a);
+        }
+
+        vvi g(n);
+        rep(i, m2) {
+            int a, b;
+            cin >> a >> b;
+            a--, b--;
+            g[a].push_back(b);
+            g[b].push_back(a);
+        }
+
+        V<bool> vis(n, false);
+        int group = 0;
+        vi groups(n, -1);
+        rep(i, n) {
+            if (!vis[i]) {
+                dothething(i, vis, groups, group, g);
+                group++;
+            }
+        }
+
+        vis.assign(n, false);
+        int count = 0;
+        int invalid = 0;
+        rep(i, n) {
+            if (!vis[i]) {
+                invalid += get(i, vis, groups, f);
+                count++;
+            }
+        }
+
+        cout << invalid + (count - group) << '\n';
+    }
+}