From 1a5e885c8f27ec3c9e48d0daf7239a1838ccaf04 Mon Sep 17 00:00:00 2001
From: Barrett Ruth <br.barrettruth@gmail.com>
Date: Tue, 8 Apr 2025 09:58:46 -0400
Subject: [PATCH] more files

---
 codeforces/874/compile_flags.txt |   1 -
 codeforces/874/f.cc              |  96 ++++++++++
 codeforces/874/f.in              |   0
 codeforces/874/g.cc              | 312 +++++++++++++++++++++++++++++++
 codeforces/874/g.in              |  21 +++
 codeforces/952/i.cc              |  99 ++++++++++
 codeforces/952/i.in              |   0
 7 files changed, 528 insertions(+), 1 deletion(-)
 create mode 100644 codeforces/874/f.cc
 create mode 100644 codeforces/874/f.in
 create mode 100644 codeforces/874/g.cc
 create mode 100644 codeforces/874/g.in
 create mode 100644 codeforces/952/i.cc
 create mode 100644 codeforces/952/i.in

diff --git a/codeforces/874/compile_flags.txt b/codeforces/874/compile_flags.txt
index 58efdbe..559f9a4 100644
--- a/codeforces/874/compile_flags.txt
+++ b/codeforces/874/compile_flags.txt
@@ -17,6 +17,5 @@
 -Wformat-overflow
 -Wformat-truncation
 -Wdouble-promotion
--Wundef
 -DLOCAL
 -std=c++23
diff --git a/codeforces/874/f.cc b/codeforces/874/f.cc
new file mode 100644
index 0000000..9b0b4f4
--- /dev/null
+++ b/codeforces/874/f.cc
@@ -0,0 +1,96 @@
+#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;
+
+template <typename T>
+[[nodiscard]] static T MIN() {
+  return std::numeric_limits<T>::min();
+}
+
+template <typename T>
+[[nodiscard]] static T MAX() {
+  return 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());
+}
+
+#define prln(...) std::println(__VA_ARGS__)
+#define pr(...) std::print(__VA_ARGS__)
+
+#ifdef LOCAL
+#define dbgln(...) std::println(__VA_ARGS__)
+#define dbg(...) std::print(__VA_ARGS__)
+#endif
+
+inline static void NO() {
+  prln("NO");
+}
+
+inline static void YES() {
+  prln("YES");
+}
+
+using ll = long long;
+using ld = long double;
+template <typename T>
+using ve = std::vector<T>;
+template <typename T, size_t N>
+using ar = std::array<T, N>;
+template <typename T1, typename T2>
+using pa = std::pair<T1, T2>;
+template <typename... Ts>
+using tu = std::tuple<Ts...>;
+template <typename... Ts>
+using dq = std::deque<Ts...>;
+template <typename... Ts>
+using qu = std::queue<Ts...>;
+template <typename... Ts>
+using pq = std::priority_queue<Ts...>;
+template <typename... Ts>
+using st = std::stack<Ts...>;
+auto lb = [](auto... args) {
+  return std::lower_bound(args...);
+};
+auto ub = [](auto... args) {
+  return std::upper_bound(args...);
+};
+
+#define ff first
+#define ss second
+#define eb emplace_back
+#define pb push_back
+#define all(x) (x).begin(), (x).end()
+#define rall(x) (x).rbegin(), (x).rend()
+//  }}}
+
+void solve() {
+  
+}
+
+int main() {  // {{{
+  cin.tie(nullptr)->sync_with_stdio(false);
+  cin.exceptions(cin.failbit);
+
+  int t = 1;
+  cin >> t;
+
+  while (t--) {
+    solve();
+  }
+
+  return 0;
+}
+// }}}
diff --git a/codeforces/874/f.in b/codeforces/874/f.in
new file mode 100644
index 0000000..e69de29
diff --git a/codeforces/874/g.cc b/codeforces/874/g.cc
new file mode 100644
index 0000000..bd3636f
--- /dev/null
+++ b/codeforces/874/g.cc
@@ -0,0 +1,312 @@
+#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;
+
+template <typename T>
+[[nodiscard]] static T MIN() {
+  return std::numeric_limits<T>::min();
+}
+
+template <typename T>
+[[nodiscard]] static T MAX() {
+  return 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());
+}
+
+#define prln(...) std::println(__VA_ARGS__)
+#define pr(...) std::print(__VA_ARGS__)
+
+#define dbgln(...) std::println(__VA_ARGS__)
+#define dbg(...) std::print(__VA_ARGS__)
+
+inline static void NO() {
+  prln("NO");
+}
+
+inline static void YES() {
+  prln("YES");
+}
+
+using ll = long long;
+using ld = long double;
+template <typename T>
+using ve = std::vector<T>;
+template <typename T, size_t N>
+using ar = std::array<T, N>;
+template <typename T1, typename T2>
+using pa = std::pair<T1, T2>;
+template <typename... Ts>
+using tu = std::tuple<Ts...>;
+template <typename... Ts>
+using dq = std::deque<Ts...>;
+template <typename... Ts>
+using qu = std::queue<Ts...>;
+template <typename... Ts>
+using pq = std::priority_queue<Ts...>;
+template <typename... Ts>
+using st = std::stack<Ts...>;
+auto lb = [](auto... args) {
+  return std::lower_bound(args...);
+};
+auto ub = [](auto... args) {
+  return std::upper_bound(args...);
+};
+
+#define ff first
+#define ss second
+#define eb emplace_back
+#define pb push_back
+#define all(x) (x).begin(), (x).end()
+#define rall(x) (x).rbegin(), (x).rend()
+//  }}}
+
+#include <ext/pb_ds/assoc_container.hpp>
+#include <ext/pb_ds/tree_policy.hpp>
+
+using namespace __gnu_pbds;
+
+// https://mirror.codeforces.com/blog/entry/124683
+
+namespace hashing {
+using i64 = std::int64_t;
+using u64 = std::uint64_t;
+static const u64 FIXED_RANDOM =
+    std::chrono::steady_clock::now().time_since_epoch().count();
+
+#if USE_AES
+std::mt19937 rd(FIXED_RANDOM);
+const __m128i KEY1{(i64)rd(), (i64)rd()};
+const __m128i KEY2{(i64)rd(), (i64)rd()};
+#endif
+
+template <class T, class D = void>
+struct custom_hash {};
+
+template <class T>
+inline void hash_combine(u64 &seed, T const &v) {
+  custom_hash<T> hasher;
+  seed ^= hasher(v) + 0x9e3779b97f4a7c15 + (seed << 12) + (seed >> 4);
+};
+
+template <class T>
+struct custom_hash<T,
+                   typename std::enable_if<std::is_integral<T>::value>::type> {
+  u64 operator()(T _x) const {
+    u64 x = _x;
+#if USE_AES
+    __m128i m{i64(u64(x) * 0xbf58476d1ce4e5b9u64), (i64)FIXED_RANDOM};
+    __m128i y = _mm_aesenc_si128(m, KEY1);
+    __m128i z = _mm_aesenc_si128(y, KEY2);
+    return z[0];
+#else
+    x += 0x9e3779b97f4a7c15 + FIXED_RANDOM;
+    x = (x ^ (x >> 30)) * 0xbf58476d1ce4e5b9;
+    x = (x ^ (x >> 27)) * 0x94d049bb133111eb;
+    return x ^ (x >> 31);
+#endif
+  }
+};
+
+template <class T>
+struct custom_hash<T, std::void_t<decltype(std::begin(std::declval<T>()))>> {
+  u64 operator()(T const &a) const {
+    u64 value = FIXED_RANDOM;
+    for (auto &x : a)
+      hash_combine(value, x);
+    return value;
+  }
+};
+
+template <class... T>
+struct custom_hash<std::tuple<T...>> {
+  u64 operator()(const std::tuple<T...> &a) const {
+    u64 value = FIXED_RANDOM;
+    std::apply(
+        [&value](T const &...args) {
+          (hash_combine(value, args), ...);
+        },
+        a);
+    return value;
+  }
+};
+
+template <class T, class U>
+struct custom_hash<std::pair<T, U>> {
+  u64 operator()(std::pair<T, U> const &a) const {
+    u64 value = FIXED_RANDOM;
+    hash_combine(value, a.first);
+    hash_combine(value, a.second);
+    return value;
+  }
+};
+};  // namespace hashing
+
+#ifdef PB_DS_ASSOC_CNTNR_HPP
+template <class Key, class Value = null_type>
+using hashtable = gp_hash_table<
+    Key, Value, hashing::custom_hash<Key>, std::equal_to<Key>,
+    direct_mask_range_hashing<>, linear_probe_fn<>,
+    hash_standard_resize_policy<hash_exponential_size_policy<>,
+                                hash_load_check_resize_trigger<>, true>>;
+
+#endif
+#ifdef PB_DS_TREE_POLICY_HPP
+template <typename T>
+using multitree = tree<T, null_type, std::less_equal<T>, rb_tree_tag,
+                       tree_order_statistics_node_update>;
+template <class Key, class Value = null_type>
+using rbtree = tree<Key, Value, std::less<Key>, rb_tree_tag,
+                    tree_order_statistics_node_update>;
+#endif
+
+void solve() {
+  size_t n;
+  cin >> n;
+  ve<ve<int>> tree(n + 1);
+  hashtable<pa<int, int>, int> edges;
+  for (size_t i = 0; i < n - 1; ++i) {
+    int u, v;
+    cin >> u >> v;
+    tree[u].eb(v);
+    tree[v].eb(u);
+    edges[{u, v}] = i + 1;
+    edges[{v, u}] = i + 1;
+  }
+
+  if (n % 3 != 0) {
+    prln("-1");
+    return;
+  }
+
+  if (n == 3) {
+    prln("0\n");
+    return;
+  }
+
+  /*
+     1. gather leaves
+     2. build up q; invariant = nodes are unused bot level
+     3. test leaves:
+        a) ^ pattern; all unused; mark all as used; pop self + neighbor, push
+par par
+          - the cut is from par to par par; save
+        b) / or \; all unused; mark all used; pop self, push par par par
+          - the cut is from par par to par par par
+
+NOTE: ignore the last (i..e root) cut in output
+
+NOTE: core assumption that tree must be binary was wrong
+problem: didn't even contest this idea
+     */
+
+  queue<int> q{{1}};
+  ve<pa<int, int>> cuts;
+  ve<int> leaves, par(n + 1, -1);
+  par[1] = 1;
+  // started 10:17
+  // TODO: no idea why the seen [] is necessary here
+  // NOTE: missed idea of deepest leaves first
+  // NOTE: missed idea/complexity of traversal, popping, and the trees first
+  // SO: what did i learn?
+
+  auto kids = [&](int u) {
+    return tree[u].size() - (u != 1);
+  };
+
+  while (!q.empty()) {
+    int size = q.size();
+    while (size--) {
+      auto u = q.front();
+      q.pop();
+      if (kids(u) == 0)
+        leaves.eb(u);
+      for (auto v : tree[u]) {
+        if (v != par[u]) {
+          par[v] = u;
+          q.emplace(v);
+        }
+      }
+    }
+  }
+
+  reverse(all(leaves));
+
+  bitset<2 * 100000 + 1> seen;
+  for (auto leaf : leaves)
+    q.emplace(leaf);
+
+  if (leaves.empty()) {
+    prln("-1");
+    return;
+  }
+
+  while (!q.empty()) {
+    auto u = q.front();
+    q.pop();
+
+    if (seen[u] || seen[par[u]]) {
+      continue;
+    }
+
+    seen[u] = seen[par[u]] = true;
+    if (kids(par[u]) == 2) {
+      for (auto v : tree[par[u]]) {
+        if (v != u && v != par[par[u]]) {
+          seen[v] = true;
+          break;
+        }
+      }
+      q.emplace(par[par[u]]);
+      if (par[u] != par[par[u]])
+        cuts.eb(par[u], par[par[u]]);
+    } else {
+      if (seen[par[par[u]]]) {
+        break;
+      }
+      seen[par[par[u]]] = true;
+      q.emplace(par[par[par[u]]]);
+      if (par[par[u]] != par[par[par[u]]])
+        cuts.eb(par[par[u]], par[par[par[u]]]);
+    }
+  }
+
+  if (cuts.empty()) {
+    prln("-1");
+    return;
+  }
+
+  prln("{}", cuts.size());
+  for (int i = 0; i < sz<int>(cuts); ++i) {
+    pr("{} ", edges[{cuts[i].ff, cuts[i].ss}]);
+  }
+  prln();
+}
+
+int main() {  // {{{
+  cin.tie(nullptr)->sync_with_stdio(false);
+  cin.exceptions(cin.failbit);
+
+  int t = 1;
+  cin >> t;
+
+  while (t--) {
+    solve();
+  }
+
+  return 0;
+}
+// }}}
diff --git a/codeforces/874/g.in b/codeforces/874/g.in
new file mode 100644
index 0000000..e07bb17
--- /dev/null
+++ b/codeforces/874/g.in
@@ -0,0 +1,21 @@
+4
+2
+1 2
+3
+1 2
+3 1
+6
+1 2
+3 1
+3 4
+3 5
+6 1
+9
+2 6
+6 9
+9 1
+9 7
+1 8
+7 3
+8 5
+4 7
diff --git a/codeforces/952/i.cc b/codeforces/952/i.cc
new file mode 100644
index 0000000..92554e4
--- /dev/null
+++ b/codeforces/952/i.cc
@@ -0,0 +1,99 @@
+#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;
+
+template <typename T>
+[[nodiscard]] static T MIN() {
+  return std::numeric_limits<T>::min();
+}
+
+template <typename T>
+[[nodiscard]] static T MAX() {
+  return 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());
+}
+
+#define prln(...) std::println(__VA_ARGS__)
+#define pr(...) std::print(__VA_ARGS__)
+
+#ifdef LOCAL
+#define dbgln(...) std::println(__VA_ARGS__)
+#define dbg(...) std::print(__VA_ARGS__)
+#else
+#define dbgln(...)
+#define dbg(...)
+#endif
+
+inline static void NO() {
+  prln("NO");
+}
+
+inline static void YES() {
+  prln("YES");
+}
+
+using ll = long long;
+using ld = long double;
+template <typename T>
+using ve = std::vector<T>;
+template <typename T, size_t N>
+using ar = std::array<T, N>;
+template <typename T1, typename T2>
+using pa = std::pair<T1, T2>;
+template <typename... Ts>
+using tu = std::tuple<Ts...>;
+template <typename... Ts>
+using dq = std::deque<Ts...>;
+template <typename... Ts>
+using qu = std::queue<Ts...>;
+template <typename... Ts>
+using pq = std::priority_queue<Ts...>;
+template <typename... Ts>
+using st = std::stack<Ts...>;
+auto lb = [](auto... args) {
+  return std::lower_bound(args...);
+};
+auto ub = [](auto... args) {
+  return std::upper_bound(args...);
+};
+
+#define ff first
+#define ss second
+#define eb emplace_back
+#define pb push_back
+#define all(x) (x).begin(), (x).end()
+#define rall(x) (x).rbegin(), (x).rend()
+//  }}}
+
+void solve() {
+  
+}
+
+int main() {  // {{{
+  cin.tie(nullptr)->sync_with_stdio(false);
+  cin.exceptions(cin.failbit);
+
+  int t = 1;
+  cin >> t;
+
+  while (t--) {
+    solve();
+  }
+
+  return 0;
+}
+// }}}
diff --git a/codeforces/952/i.in b/codeforces/952/i.in
new file mode 100644
index 0000000..e69de29