Problem p02928 (C++)

Buggy submission (status: Time Limit Exceeded):
#include <bits/stdc++.h>
#define all(v) v.begin(), v.end()
#define rall(v) v.rbegin(), v.rend()
#define rep(i, n) for (int i = 0; i < (int)(n); i++)
#define codefor                                                                \
  int test;                                                                    \
  scanf("%d", &test);                                                          \
  while (test--)
#define yn(ans)                                                                \
  if (ans)                                                                     \
    printf("Yes\n");                                                           \
  else                                                                         \
    printf("No\n")
#define YN(ans)                                                                \
  if (ans)                                                                     \
    printf("YES\n");                                                           \
  else                                                                         \
    printf("NO\n")
#define umap unordered_map
#define uset unordered_set
using namespace std;
using ll = long long;
const int MOD = 1000000007;
// 入力系
void scan(int &a) { scanf("%d", &a); }
void scan(long long &a) { scanf("%lld", &a); }
template <class T> void scan(T &a) { cin >> a; }
template <class T> void scan(vector<T> &vec) {
  for (auto &&it : vec)
    scan(it);
}
void in() {}
template <class Head, class... Tail> void in(Head &head, Tail &...tail) {
  scan(head);
  in(tail...);
}
// 出力系
void print(const int &a) { printf("%d", a); }
void print(const long long &a) { printf("%lld", a); }
void print(const double &a) { printf("%.15lf", a); }
template <class T> void print(const T &a) { cout << a; }
template <class T> void print(const vector<T> &vec) {
  if (vec.empty())
    return;
  print(vec[0]);
  for (auto it = vec.begin(); ++it != vec.end();) {
    putchar(' ');
    print(*it);
  }
}
void out() { putchar('\n'); }
template <class T> void out(const T &t) {
  print(t);
  putchar('\n');
}
template <class Head, class... Tail>
void out(const Head &head, const Tail &...tail) {
  print(head);
  putchar(' ');
  out(tail...);
}
// デバッグ系
template <class T> void dprint(const T &a) { cerr << a; }
template <class T> void dprint(const vector<T> &vec) {
  if (vec.empty())
    return;
  cerr << vec[0];
  for (auto it = vec.begin(); ++it != vec.end();) {
    cerr << " " << *it;
  }
}
void debug() { cerr << endl; }
template <class T> void debug(const T &t) {
  dprint(t);
  cerr << endl;
}
template <class Head, class... Tail>
void debug(const Head &head, const Tail &...tail) {
  dprint(head);
  cerr << " ";
  debug(tail...);
}

int main() {
  long long int n, k;
  in(n, k);
  vector<ll> a(n);
  in(a);
  ll ans = 0;
  for (int i = 0; i < n - 1; i++) {
    for (int j = i + 1; j < n; j++) {
      if (a[i] > a[j])
        ans++;
    }
  }
  ll ans2 = ans * k;
  ans = 0;
  for (int i = 0; i < n; i++) {
    for (int j = 0; j < n; j++) {
      if (a[i] > a[j])
        ans++;
    }
  }
  for (k--; k >= 1; k--) {
    ans2 += (ll)ans * k;
    if (ans2 > MOD)
      ans2 %= MOD;
  }
  out(ans2);
}

Fixed submission:
#include <bits/stdc++.h>
#define all(v) v.begin(), v.end()
#define rall(v) v.rbegin(), v.rend()
#define rep(i, n) for (int i = 0; i < (int)(n); i++)
#define codefor                                                                \
  int test;                                                                    \
  scanf("%d", &test);                                                          \
  while (test--)
#define yn(ans)                                                                \
  if (ans)                                                                     \
    printf("Yes\n");                                                           \
  else                                                                         \
    printf("No\n")
#define YN(ans)                                                                \
  if (ans)                                                                     \
    printf("YES\n");                                                           \
  else                                                                         \
    printf("NO\n")
#define umap unordered_map
#define uset unordered_set
using namespace std;
using ll = long long;
const int MOD = 1000000007;
// 入力系
void scan(int &a) { scanf("%d", &a); }
void scan(long long &a) { scanf("%lld", &a); }
template <class T> void scan(T &a) { cin >> a; }
template <class T> void scan(vector<T> &vec) {
  for (auto &&it : vec)
    scan(it);
}
void in() {}
template <class Head, class... Tail> void in(Head &head, Tail &...tail) {
  scan(head);
  in(tail...);
}
// 出力系
void print(const int &a) { printf("%d", a); }
void print(const long long &a) { printf("%lld", a); }
void print(const double &a) { printf("%.15lf", a); }
template <class T> void print(const T &a) { cout << a; }
template <class T> void print(const vector<T> &vec) {
  if (vec.empty())
    return;
  print(vec[0]);
  for (auto it = vec.begin(); ++it != vec.end();) {
    putchar(' ');
    print(*it);
  }
}
void out() { putchar('\n'); }
template <class T> void out(const T &t) {
  print(t);
  putchar('\n');
}
template <class Head, class... Tail>
void out(const Head &head, const Tail &...tail) {
  print(head);
  putchar(' ');
  out(tail...);
}
// デバッグ系
template <class T> void dprint(const T &a) { cerr << a; }
template <class T> void dprint(const vector<T> &vec) {
  if (vec.empty())
    return;
  cerr << vec[0];
  for (auto it = vec.begin(); ++it != vec.end();) {
    cerr << " " << *it;
  }
}
void debug() { cerr << endl; }
template <class T> void debug(const T &t) {
  dprint(t);
  cerr << endl;
}
template <class Head, class... Tail>
void debug(const Head &head, const Tail &...tail) {
  dprint(head);
  cerr << " ";
  debug(tail...);
}

int main() {
  long long int n, k;
  in(n, k);
  vector<ll> a(n);
  in(a);
  ll ans = 0;
  for (int i = 0; i < n - 1; i++) {
    for (int j = i + 1; j < n; j++) {
      if (a[i] > a[j])
        ans++;
    }
  }
  ll ans2 = ans * k;
  ans = 0;
  for (int i = 0; i < n; i++) {
    for (int j = 0; j < n; j++) {
      if (a[i] > a[j])
        ans++;
    }
  }
  ans2 += (ll)ans * ((k * (k - 1) / 2) % MOD);
  ans2 %= MOD;
  out(ans2);
}