feat: 806

codeforces/918/f.cc

@@ -0,0 +1,114 @@
+#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
+//  }}}
+
+i64 inv_merge(vector<i64>& a, vector<i64>& tmp) {
+  if (r - l <= 1)
+    return 0;
+  int m = (l + r) >> 1;
+  i64 ans = inv_merge(a, tmp, l, m) + inv_merge(a, tmp, m, r);
+  int i = l, j = m, k = l;
+  while (i < m || j < r) {
+    if (j == r || (i < m && a[i] <= a[j]))
+      tmp[k++] = a[i++];
+    else {
+      tmp[k++] = a[j++];
+      ans += (m - i);
+    }
+  }
+  return ans;
+}
+
+void solve() {
+  // NOTE: erroneosouyl thought was interval overlaps (even that took too long
+  // to code) should've stayed at it and continued, but was tired/acted tired
+  // consider the problem statemnt & examples more slowly
+  // simplifcation: count the inversions
+  i32 n;
+  cin >> n;
+  vector<pair<i64, i64>> p(n);
+  for (i32 i = 0; i < n; ++i)
+    cin >> p[i].first >> p[i].second;
+  sort(all(p));
+  vector<i64> b(n), tmp(n);
+  for (i32 i = 0; i < n; ++i)
+    b[i] = p[i].second;
+  println("{}", inv_merge(b, tmp, 0, n));
+}
+
+int main() {  // {{{
+  std::cin.exceptions(std::cin.failbit);
+
+#ifdef LOCAL
+  std::cerr.rdbuf(std::cout.rdbuf());
+  std::cout.setf(std::ios::unitbuf);
+  std::cerr.setf(std::ios::unitbuf);
+#else
+  std::cin.tie(nullptr)->sync_with_stdio(false);
+#endif
+
+  u32 tc = 1;
+  std::cin >> tc;
+
+  for (u32 t = 0; t < tc; ++t) {
+    solve();
+  }
+
+  return 0;
+}
+// }}}