Problem p04021 (C++)

Buggy submission (status: Time Limit Exceeded):
#include <bits/stdc++.h>
using namespace std;
#define FOR(i, o, n) for (long long i = o; i < n; i++)
#define oneforall                                                              \
  ios::sync_with_stdio(false);                                                 \
  cin.tie(0);
#define all(v) (v).begin(), (v).end()
#define ini(...)                                                               \
  int __VA_ARGS__;                                                             \
  in(__VA_ARGS__)
#define inl(...)                                                               \
  long long __VA_ARGS__;                                                       \
  in(__VA_ARGS__)
#define ins(...)                                                               \
  string __VA_ARGS__;                                                          \
  in(__VA_ARGS__)
#define int long long
const long long INF = 1e18;
void in() {}
template <typename T, class... U> void in(T &t, U &...u) {
  cin >> t;
  in(u...);
}
void out() { cout << "\n"; }
template <typename T, class... U> void out(const T &t, const U &...u) {
  cout << t;
  if (sizeof...(u))
    cout << " ";
  out(u...);
}
typedef vector<int> vi;
typedef vector<long long> vl;
typedef long long ll;
typedef vector<pair<long, long>> vpll;
typedef vector<pair<int, int>> vpii;
#define FORR(x, arr) for (auto &x : arr)

bool isprime(int x) {
  for (int i = 2; i * i <= x; i++) {
    if (x % i == 0)
      return false;
  }
  return x != 1;
}
int gcd(int a, int b) {
  if (a == 0)
    return b;
  if (b == 0)
    return a;

  if (a == b)
    return a;

  if (a > b)
    return gcd(a - b, b);
  return gcd(a, b - a);
}

// 3111111111111111111111111111111

void solve() {

  ini(n);
  vi morty;
  vi mortysort;
  FOR(i, 0, n) {
    ini(x);
    morty.push_back(x);
    mortysort.push_back(x);
  }
  sort(all(mortysort));
  int tmp = 0;
  FOR(i, 0, n) {
    int x1 = find(all(mortysort), morty[i]) - mortysort.begin();
    if ((x1 + i) % 2)
      tmp++;
  }
  out(tmp / 2);
}

int32_t main() {
  oneforall oneforall oneforall oneforall oneforall oneforall oneforall
      oneforall oneforall oneforall oneforall oneforall oneforall oneforall

      solve();

  return 0;
}

Fixed submission:
#include <bits/stdc++.h>
using namespace std;
#define FOR(i, o, n) for (long long i = o; i < n; i++)
#define oneforall                                                              \
  ios::sync_with_stdio(false);                                                 \
  cin.tie(0);
#define all(v) (v).begin(), (v).end()
#define ini(...)                                                               \
  int __VA_ARGS__;                                                             \
  in(__VA_ARGS__)
#define inl(...)                                                               \
  long long __VA_ARGS__;                                                       \
  in(__VA_ARGS__)
#define ins(...)                                                               \
  string __VA_ARGS__;                                                          \
  in(__VA_ARGS__)
#define int long long
const long long INF = 1e18;
void in() {}
template <typename T, class... U> void in(T &t, U &...u) {
  cin >> t;
  in(u...);
}
void out() { cout << "\n"; }
template <typename T, class... U> void out(const T &t, const U &...u) {
  cout << t;
  if (sizeof...(u))
    cout << " ";
  out(u...);
}
typedef vector<int> vi;
typedef vector<long long> vl;
typedef long long ll;
typedef vector<pair<long, long>> vpll;
typedef vector<pair<int, int>> vpii;
#define FORR(x, arr) for (auto &x : arr)

bool isprime(int x) {
  for (int i = 2; i * i <= x; i++) {
    if (x % i == 0)
      return false;
  }
  return x != 1;
}
int gcd(int a, int b) {
  if (a == 0)
    return b;
  if (b == 0)
    return a;

  if (a == b)
    return a;

  if (a > b)
    return gcd(a - b, b);
  return gcd(a, b - a);
}

// 3111111111111111111111111111111

void solve() {

  ini(n);
  vi morty;
  vi mortysort;
  FOR(i, 0, n) {
    ini(x);
    morty.push_back(x);
    mortysort.push_back(x);
  }
  sort(all(mortysort));
  int tmp = 0;
  FOR(i, 0, n) {
    int x1 = lower_bound(all(mortysort), morty[i]) - mortysort.begin();
    if ((x1 + i) % 2)
      tmp++;
  }
  out(tmp / 2);
}

int32_t main() {
  oneforall oneforall oneforall oneforall oneforall oneforall oneforall
      oneforall oneforall oneforall oneforall oneforall oneforall oneforall

      solve();

  return 0;
}