fea: more contests

codeforces/903/f.cc

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+#include <bits/stdc++.h>  // {{{
+
+// https://codeforces.com/blog/entry/96344
+
+#pragma GCC optimize("O2,unroll-loops")
+#pragma GCC target("avx2,bmi,bmi2,lzcnt,popcnt")
+
+using namespace std;
+
+using i32 = int32_t;
+using u32 = uint32_t;
+using i64 = int64_t;
+using u64 = uint64_t;
+using f64 = double;
+using f128 = long double;
+
+#if __cplusplus >= 202002L
+template <typename T>
+constexpr T MIN = std::numeric_limits<T>::min();
+
+template <typename T>
+constexpr T MAX = std::numeric_limits<T>::max();
+
+template <typename T>
+[[nodiscard]] static T sc(auto&& x) {
+  return static_cast<T>(x);
+}
+
+template <typename T>
+[[nodiscard]] static T sz(auto&& x) {
+  return static_cast<T>(x.size());
+}
+#endif
+
+static void NO() {
+  std::cout << "NO\n";
+}
+
+static void YES() {
+  std::cout << "YES\n";
+}
+
+template <typename T>
+using vec = std::vector<T>;
+
+#define all(x) (x).begin(), (x).end()
+#define rall(x) (x).rbegin(), (x).rend()
+#define ff first
+#define ss second
+
+#ifdef LOCAL
+#define db(...) std::print(__VA_ARGS__)
+#define dbln(...) std::println(__VA_ARGS__)
+#else
+#define db(...)
+#define dbln(...)
+#endif
+//  }}}
+
+const u32 MAXN = 2 * 1e5 + 1;
+bitset<MAXN> marked, seen;
+vector<vector<u32>> tree(MAXN);
+deque<u32> q;
+
+void solve() {
+  u32 n, k;
+  cin >> n >> k;
+
+  marked.reset();
+  tree.assign(n + 1, vector<u32>());
+
+  u32 node;
+  for (u32 i = 0; i < k; ++i) {
+    cin >> node;
+    marked[node] = true;
+  }
+
+  u32 u, v;
+  for (u32 i = 0; i < n - 1; ++i) {
+    cin >> u >> v;
+    tree[u].emplace_back(v);
+    tree[v].emplace_back(u);
+  }
+
+  q.clear();
+  q.push_back(node);
+  seen.reset();
+  u32 last = node;
+
+  while (!q.empty()) {
+    auto top = q.front();
+    q.pop_front();
+    seen[top] = true;
+    if (marked[top])
+      last = top;
+
+    for (auto& neighbor : tree[top]) {
+      if (!seen[neighbor]) {
+        q.push_back(neighbor);
+      }
+    }
+  }
+
+  q.clear();
+  q.push_back(last);
+  seen.reset();
+  u32 ans = 0, d = 0;
+
+  while (!q.empty()) {
+    ++d;
+    u32 size = q.size();
+    for (u32 i = 0; i < size; ++i) {
+      auto top = q.front();
+      q.pop_front();
+      if (marked[top])
+        ans = max(ans, d);
+      seen[top] = true;
+      for (auto& neighbor : tree[top]) {
+        if (!seen[neighbor]) {
+          q.push_back(neighbor);
+        }
+      }
+    }
+  }
+
+  cout << ans / 2 << endl;
+}
+
+int main() {  // {{{
+  cin.tie(nullptr)->sync_with_stdio(false);
+  cin.exceptions(cin.failbit);
+
+  u32 tc = 1;
+  cin >> tc;
+
+  for (u32 t = 0; t < tc; ++t) {
+    solve();
+  }
+
+  return 0;
+}
+// }}}