Language: C++

#include<bits/stdc++.h>
#pragma GCC optimize("Ofast")
using namespace std;
#define all(x) (x).begin(),(x).end()
typedef long long ll;
#define rep(i,n) for(ll i=0, i##_len=(n); i<i##_len; ++i)
#define REP(i,num,n) for(ll i=num, i##_len=(n); i<i##_len; ++i)
template<class T>bool chmax(T &a, const T &b) { if (a<b) { a=b; return 1; } return 0; }
template<class T>bool chmin(T &a, const T &b) { if (b<a) { a=b; return 1; } return 0; }
#define print(x) cout << (x) << endl;
#define sz(x) int(x.size())
 
ll gcd(ll a,ll b){return b?gcd(b,a%b):a;}
const ll LLINF = 1LL<<60;
const int INF = 1<<29;

 
const int dx[8] = {1, 0, -1, 0, 1, -1, -1, 1};
const int dy[8] = {0, 1, 0, -1, 1, 1, -1, -1};

constexpr ll mod = 1e9+7;

template< int mod >
struct ModInt {
  int x;

  ModInt() : x(0) {}

  ModInt(int64_t y) : x(y >= 0 ? y % mod : (mod - (-y) % mod) % mod) {}

  ModInt &operator+=(const ModInt &p) {
   if((x += p.x) >= mod) x -= mod;
   return *this;
 }

  ModInt &operator-=(const ModInt &p) {
   if((x += mod - p.x) >= mod) x -= mod;
   return *this;
  }

  ModInt &operator*=(const ModInt &p) {
   x = (int) (1LL * x * p.x % mod);
   return *this;
  }

  ModInt &operator/=(const ModInt &p) {
   *this *= p.inverse();
   return *this;
  }

  ModInt operator-() const { return ModInt(-x); }

  ModInt operator+(const ModInt &p) const { return ModInt(*this) += p; }

  ModInt operator-(const ModInt &p) const { return ModInt(*this) -= p; }

  ModInt operator*(const ModInt &p) const { return ModInt(*this) *= p; }

  ModInt operator/(const ModInt &p) const { return ModInt(*this) /= p; }

  bool operator==(const ModInt &p) const { return x == p.x; }

  bool operator!=(const ModInt &p) const { return x != p.x; }

  ModInt inverse() const {
   int a = x, b = mod, u = 1, v = 0, t;
   while(b > 0) {
     t = a / b;
     swap(a -= t * b, b);
     swap(u -= t * v, v);
   }
   return ModInt(u);
  }

  ModInt pow(int64_t n) const {
   ModInt ret(1), mul(x);
   while(n > 0) {
     if(n & 1) ret *= mul;
     mul *= mul;
     n >>= 1;
   }
   return ret;
  }

  friend ostream &operator<<(ostream &os, const ModInt &p) {
   return os << p.x;
  }

  friend istream &operator>>(istream &is, ModInt &a) {
   int64_t t;
   is >> t;
   a = ModInt< mod >(t);
   return (is);
  }

  static int get_mod() { return mod; }
};

using modint = ModInt< mod >;

int main(){
  ll N,K;
  cin >> N >> K;
  
  vector<ll> S1(N);
  vector<ll> S2(N);
  
  vector<ll> A(N);
  
  rep(i,N){
    ll a;
    cin >> A[i];
  }
  
  rep(i,N){
    ll count1 = 0;
    ll count2 = 0;
    rep(j,N){
      if(A[i]>A[j]){
        count1 += 1;
        if(j>i)count2 += 1;
      }
    }
    S1[i] = count1;
    S2[i] = count2;
  }
  
  ll sum1 = 0;
  ll sum2 = 0;
  
  for(ll n: S1){
    sum1 += n;
  }
  
  for(ll n: S2){
    sum2 += n;
  }
  
  // ll ans = ( ( (sum2%MOD) * (K%MOD) )%MOD ) + ( (((sum1%MOD)*(((K-1)%MOD)*(K%MOD))%MOD)%MOD)*modinv(2, MOD)%MOD );
  ll ans = 0;
  
  modint s1,s2,k,km1,n2;
  s1 = sum1;
  s2 = sum2;
  k = K;
  km1 = K-1;
  n2 = 2;

  ans = ( ( sum2 * K )%MOD ) + ( ((sum1*((K-1)/2*K)%MOD)%MOD) );
  ans = 1LL * (s2 * k + s1*km1*k/n2);
  
  cout << ans << endl;




  return 0;
}


Compiler output:
a.cc: In function 'int main()':
a.cc:149:24: error: 'MOD' was not declared in this scope
  149 |   ans = ( ( sum2 * K )%MOD ) + ( ((sum1*((K-1)/2*K)%MOD)%MOD) );
      |                        ^~~
a.cc:150:13: error: no match for 'operator*' (operand types are 'long long int' and 'ModInt<1000000007>')
  150 |   ans = 1LL * (s2 * k + s1*km1*k/n2);
      |         ~~~ ^ ~~~~~~~~~~~~~~~~~~~~~~
      |         |             |
      |         long long int ModInt<1000000007>
In file included from /usr/include/c++/14/ccomplex:39,
                 from /usr/include/x86_64-linux-gnu/c++/14/bits/stdc++.h:127,
                 from a.cc:1:
/usr/include/c++/14/complex:400:5: note: candidate: 'template<class _Tp> std::complex<_Tp> std::operator*(const complex<_Tp>&, const complex<_Tp>&)'
  400 |     operator*(const complex<_Tp>& __x, const complex<_Tp>& __y)
      |     ^~~~~~~~
/usr/include/c++/14/complex:400:5: note:   template argument deduction/substitution failed:
a.cc:150:36: note:   mismatched types 'const std::complex<_Tp>' and 'long long int'
  150 |   ans = 1LL * (s2 * k + s1*km1*k/n2);
      |                                    ^
/usr/include/c++/14/complex:409:5: note: candidate: 'template<class _Tp> std::complex<_Tp> std::operator*(const complex<_Tp>&, const _Tp&)'
  409 |     operator*(const complex<_Tp>& __x, const _Tp& __y)
      |     ^~~~~~~~
/usr/include/c++/14/complex:409:5: note:   template argument deduction/substitution failed:
a.cc:150:36: note:   mismatched types 'const std::complex<_Tp>' and 'long long int'
  150 |   ans = 1LL * (s2 * k + s1*km1*k/n2);
      |                                    ^
/usr/include/c++/14/complex:418:5: note: candidate: 'template<class _Tp> std::complex<_Tp> std::operator*(const _Tp&, const complex<_Tp>&)'
  418 |     operator*(const _Tp& __x, const complex<_Tp>& __y)
      |     ^~~~~~~~
/usr/include/c++/14/complex:418:5: note:   template argument deduction/substitution failed:
a.cc:150:36: note:   'ModInt<1000000007>' is not derived from 'const std::complex<_Tp>'
  150 |   ans = 1LL * (s2 * k + s1*km1*k/n2);
      |                                    ^
In file included from /usr/include/c++/14/valarray:605,
                 from /usr/include/x86_64-linux-gnu/c++/14/bits/stdc++.h:166:
/usr/include/c++/14/bits/valarray_after.h:407:5: note: candidate: 'template<class _Dom1, class _Dom2> std::_Expr<std::__detail::_BinClos<std::__multiplies, std::_Expr, std::_Expr, _Dom1, _Dom2>, typename std::__fun<std::__multiplies, typename _Dom1::value_type>::result_type> std::operator*(const _Expr<_Dom1, typename _Dom1::value_type>&, const _Expr<_Dom2, typename _Dom2::value_type>&)'
  407 |     _DEFINE_EXPR_BINARY_OPERATOR(*, struct std::__multiplies)
      |     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/14/bits/valarray_after.h:407:5: note:   template argument deduction/substitution failed:
a.cc:150:36: note:   mismatched types 'const std::_Expr<_Dom1, typename _Dom1::value_type>' and 'long long int'
  150 |   ans = 1LL * (s2 * k + s1*km1*k/n2);
      |                                    ^
/usr/include/c++/14/bits/valarray_after.h:407:5: note: candidate: 'template<class _Dom> std::_Expr<std::__detail::_BinClos<std::__multiplies, std::_Expr, std::_Constant, _Dom, typename _Dom::value_type>, typename std::__fun<std::__multiplies, typename _Dom1::value_type>::result_type> std::operator*(const _Expr<_Dom1, typename _Dom1::value_type>&, const typename _Dom::value_type&)'
  407 |     _DEFINE_EXPR_BINARY_OPERATOR(*, struct std::__multiplies)
      |     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/14/bits/valarray_after.h:407:5: note:   template argument deduction/substitution failed:
a.cc:150:36: note:   mismatched types 'const std::_Expr<_Dom1, typename _Dom1::value_type>' and 'long long int'
  150 |   ans = 1LL * (s2 * k + s1*km1*k/n2);
      |                                    ^
/usr/include/c++/14/bits/valarray_after.h:407:5: note: candidate: 'template<class _Dom> std::_Expr<std::__detail::_BinClos<std::__multiplies, std::_Constant, std::_Expr, typename _Dom::value_type, _Dom>, typename std::__fun<std::__multiplies, typename _Dom1::value_type>::result_type> std::operator*(const typename _Dom::value_type&, const _Expr<_Dom1, typename _Dom1::value_type>&)'
  407 |     _DEFINE_EXPR_BINARY_OPERATOR(*, struct std::__multiplies)
      |     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/14/bits/valarray_after.h:407:5: note:   template argument deduction/substitution failed:
a.cc:150:36: note:   'ModInt<1000000007>' is not derived from 'const std::_Expr<_Dom1, typename _Dom1::value_type>'
  150 |   ans = 1LL * (s2 * k + s1*km1*k/n2);
      |                                    ^
/usr/include/c++/14/bits/valarray_after.h:407:5: note: candidate: 'template<class _Dom> std::_Expr<std::__detail::_BinClos<std::__multiplies, std::_Expr, std::_ValArray, _Dom, typename _Dom::value_type>, typename std::__fun<std::__multiplies, typename _Dom1::value_type>::result_type> std::operator*(const _Expr<_Dom1, typename _Dom1::value_type>&, const valarray<typename _Dom::value_type>&)'
  407 |     _DEFINE_EXPR_BINARY_OPERATOR(*, struct std::__multiplies)
      |     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/14/bits/valarray_after.h:407:5: note:   template argument deduction/substitution failed:
a.cc:150:36: note:   mismatched types 'const std::_Expr<_Dom1, typename _Dom1::value_type>' and 'long long int'
  150 |   ans = 1LL * (s2 * k + s1*km1*k/n2);
      |                                    ^
/usr/include/c++/14/bits/valarray_after.h:407:5: note: candidate: 'template<class _Dom> std::_Expr<std::__detail::_BinClos<std::__multiplies, std::_ValArray, std::_Expr, typename _Dom::value_type, _Dom>, typename std::__fun<std::__multiplies, typename _Dom1::value_type>::result_type> std::operator*(const valarray<typename _Dom::value_type>&, const _Expr<_Dom1, typename _Dom1::value_type>&)'
  407 |     _DEFINE_EXPR_BINARY_OPERATOR(*, struct std::__multiplies)
      |     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/14/bits/valarray_after.h:407:5: note:   template argument deduction/substitution failed:
a.cc:150:36: note:   'ModInt<1000000007>' is not derived from 'const std::_Expr<_Dom1, typename _Dom1::value_type>'
  150 |   ans = 1LL * (s2 * k + s1*km1*k/n2);
      |                                    ^
/usr/include/c++/14/valarray:1198:1: note: candidate: 'template<class _Tp> std::_Expr<std::__detail::_BinClos<std::__multiplies, std::_ValArray, std::_ValArray, _Tp, _Tp>, typename std::__fun<std::__multiplies, _Tp>::result_type> std::operator*(const valarray<_Tp>&, const valarray<_Tp>&)'
 1198 | _DEFINE_BINARY_OPERATOR(*, __multiplies)
      | ^~~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/14/valarray:1198:1: note:   template argument deduction/substitution failed:
a.cc:150:36: note:   mismatched types 'const std::valarray<_Tp>' and 'long long int'
  150 |   ans = 1LL * (s2 * k + s1*km1*k/n2);
      |                                    ^
/usr/include/c++/14/valarray:1198:1: note: candidate: 'template<class _Tp> std::_Expr<std::__detail::_BinClos<std::__multiplies, std::_ValArray, std::_Constant, _Tp, _Tp>, typename std::__fun<std::__multiplies, _Tp>::result_type> std::operator*(const valarray<_Tp>&, const typename valarray<_Tp>::value_type&)'
 1198 | _DEFINE_BINARY_OPERATOR(*, __multiplies)
      | ^~~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/14/valarray:1198:1: note:   template argument deduction/substitution failed:
a.cc:150:36: note:   mismatched types 'const std::valarray<_Tp>' and 'long long int'
  150 |   ans = 1LL * (s2 * k + s1*km1*k/n2);
      |                                    ^
/usr/include/c++/14/valarray:1198:1: note: candidate: 'template<class _Tp> std::_Expr<std::__detail::_BinClos<std::__multiplies, std::_Constant, std::_ValArray, _Tp, _Tp>, typename std::__fun<std::__multiplies, _Tp>::result_type> std::operator*(const typename valarray<_Tp>::value_type&, const valarray<_Tp>&)'
 1198 | _DEFINE_BINARY_OPERATOR(*, __multiplies)
      | ^~~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/14/valarray:1198:1: note:   template argument deduction/substitution failed:
a.cc:150:36: note:   'ModInt<1000000007>' is not derived from 'const std::valarray<_Tp>'
  150 |   ans = 1LL * (s2 * k + s1*km1*k/n2);
      |                                    ^