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Codeforces Round 1042 (Div. 3)/D. Arboris Contractio.cpp

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+/* Problem URL: https://codeforces.com/contest/2131/problem/D */
+
+#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;
+        cin >> n;
+
+        vvi graph(n);
+        rep(i, n - 1) {
+            int a, b;
+            cin >> a >> b;
+            a--, b--;
+
+            graph[a].push_back(b);
+            graph[b].push_back(a);
+        }
+
+        int dim = 0;
+
+        auto bfs = [&](int i) {
+            int inf = INT32_MAX >> 1;
+            vi dis(n, inf);
+            int ans = 0;
+
+            queue<int> q;
+            q.push(i);
+            dis[i] = 0;
+
+            while (!q.empty()) {
+                i = q.front();
+                q.pop();
+
+                for (auto j : graph[i]) {
+                    if (dis[j] > dis[i] + 1) {
+                        dis[j] = dis[i] + 1;
+                        dim = dis[j];
+                        q.push(j);
+                        ans = j;
+                    }
+                }
+            }
+
+            return ans;
+        };
+
+        int tmp = bfs(0);
+        int fds = bfs(tmp);
+
+        if (dim <= 2) {
+            cout << "0\n";
+            continue;
+        }
+
+        vi count(n);
+
+        int total = 0;
+
+        rep(i, n) {
+            if (graph[i].size() == 1) {
+                count[graph[i][0]]++;
+                total++;
+            }
+        }
+
+        int ans = total;
+
+        rep(i, n) {
+            rmin(ans, total - count[i]);
+        }
+
+        cout << ans << '\n';
+    }
+}