Language: C++

#include<bits/stdc++.h>
using namespace std;
using ll = long long;
using i64 = int_fast64_t;
constexpr i64 MAX = 510000;
constexpr i64 MOD = 1000000007;
i64 fac[MAX], finv[MAX], inv[MAX];
template <i64 modulus>
class modcal
{

public:
  i64 a;

  constexpr modcal(const i64 x = 0) noexcept : a(x % modulus) {}
  constexpr i64 &value() noexcept { return a; }
  constexpr const i64 &value() const noexcept { return a; }
  constexpr modcal operator+(const modcal rhs) const noexcept
  {
    return modcal(*this) += rhs;
  }
  constexpr modcal operator-(const modcal rhs) const noexcept
  {
    return modcal(*this) -= rhs;
  }
  constexpr modcal operator*(const modcal rhs) const noexcept
  {
    return modcal(*this) *= rhs;
  }
  constexpr modcal operator/(const modcal rhs) noexcept
  {
    return modcal(*this) /= rhs;
  }
  constexpr modcal &operator+=(const modcal rhs) noexcept
  {
    a += rhs.a;
    if (a >= modulus)
    {
      a -= modulus;
    }
    return *this;
  }
  constexpr modcal &operator-=(const modcal rhs) noexcept
  {
    if (a < rhs.a)
    {
      a += modulus;
    }
    a -= rhs.a;
    return *this;
  }
  constexpr modcal &operator*=(const modcal rhs) noexcept
  {
    a = a * rhs.a % modulus;
    return *this;
  }
  constexpr modcal &operator/=(modcal rhs) noexcept
  {
    i64 exp = modulus - 2;
    while (exp)
    {
      if (exp % 2)
      {
        *this *= rhs;
      }
      rhs *= rhs;
      exp /= 2;
    }
    return *this;
  }

  void COMninit()
  {
    fac[0] = fac[1] = 1;
    finv[0] = finv[1] = 1;
    inv[1] = 1;
    for (int i = 2; i < MAX; i++)
    {
      fac[i] = fac[i - 1] * i % modulus;
      inv[i] = MOD - inv[modulus % i] * (modulus / i) % modulus;
      finv[i] = finv[i - 1] * inv[i] % modulus;
    }
  }
  i64 COMn(i64 n, i64 k)
  {
    if (n < k)
      return 0;
    if (n < 0 || k < 0)
      return 0;
    return fac[n] * (finv[k] * finv[n - k] % modulus) % modulus;
  }
  constexpr modcal<1000000007> modpow(const modcal<1000000007> &a, i64 n)
  {
    if (n == 0)
      return 1;
    auto t = modpow(a, n / 2);
    t = t * t;
    if (n & 1)
      t = t * a;
    return t;
  }
};
using modc = modcal<1000000007>;
int main(){
ios::sync_with_stdio(false);
std::cin.tie(nullptr);
modc n;
cin >> n.a;
map<pair<ll,ll>,ll> mp;
set<pair<ll,ll>> st;
for(ll i = 0; i < n.a; i++){
    ll a,b;
    cin >> a >> b;
    if(a < b){
    mp[make_pair(-b,a)]++;
    }
    else
    {
        mp[make_pair(a,b)]++;
        st.insert(a,b);
    }
}
modc a = 0;
a.COMninit();
modc cnt = a.COMn(n.a,2);
for(auto v:st){
    cnt.a -= mp[make_pair(v.first,v.second)] * mp[make_pair(-v.second,v.first)];
}
    cout << cnt.a - mp[make_pair(0,0)] * (n.a - mp[make_pair(0,0)])<< endl;
}

Compiler output:
In file included from /usr/include/c++/14/set:63,
                 from /usr/include/x86_64-linux-gnu/c++/14/bits/stdc++.h:158,
                 from a.cc:1:
/usr/include/c++/14/bits/stl_set.h: In instantiation of 'void std::set<_Key, _Compare, _Alloc>::insert(_InputIterator, _InputIterator) [with _InputIterator = long long int; _Key = std::pair<long long int, long long int>; _Compare = std::less<std::pair<long long int, long long int> >; _Alloc = std::allocator<std::pair<long long int, long long int> >]':
a.cc:120:18:   required from here
  120 |         st.insert(a,b);
      |         ~~~~~~~~~^~~~~
/usr/include/c++/14/bits/stl_set.h:569:38: error: no matching function for call to 'std::_Rb_tree<std::pair<long long int, long long int>, std::pair<long long int, long long int>, std::_Identity<std::pair<long long int, long long int> >, std::less<std::pair<long long int, long long int> >, std::allocator<std::pair<long long int, long long int> > >::_M_insert_range_unique(long long int&, long long int&)'
  569 |         { _M_t._M_insert_range_unique(__first, __last); }
      |           ~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~
In file included from /usr/include/c++/14/map:62,
                 from /usr/include/x86_64-linux-gnu/c++/14/bits/stdc++.h:152:
/usr/include/c++/14/bits/stl_tree.h:1096:9: note: candidate: 'template<class _InputIterator> std::__enable_if_t<((bool)std::is_same<_Val, typename std::iterator_traits<_InputIterator>::value_type>::value)> std::_Rb_tree<_Key, _Val, _KeyOfValue, _Compare, _Alloc>::_M_insert_range_unique(_InputIterator, _InputIterator) [with _Key = std::pair<long long int, long long int>; _Val = std::pair<long long int, long long int>; _KeyOfValue = std::_Identity<std::pair<long long int, long long int> >; _Compare = std::less<std::pair<long long int, long long int> >; _Alloc = std::allocator<std::pair<long long int, long long int> >]'
 1096 |         _M_insert_range_unique(_InputIterator __first, _InputIterator __last)
      |         ^~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/14/bits/stl_tree.h:1096:9: note:   template argument deduction/substitution failed:
/usr/include/c++/14/bits/stl_tree.h: In substitution of 'template<class _InputIterator> std::__enable_if_t<((bool)std::is_same<std::pair<long long int, long long int>, typename std::iterator_traits< <template-parameter-1-1> >::value_type>::value), void> std::_Rb_tree<std::pair<long long int, long long int>, std::pair<long long int, long long int>, std::_Identity<std::pair<long long int, long long int> >, std::less<std::pair<long long int, long long int> >, std::allocator<std::pair<long long int, long long int> > >::_M_insert_range_unique(_InputIterator, _InputIterator) [with _InputIterator = long long int]':
/usr/include/c++/14/bits/stl_set.h:569:31:   required from 'void std::set<_Key, _Compare, _Alloc>::insert(_InputIterator, _InputIterator) [with _InputIterator = long long int; _Key = std::pair<long long int, long long int>; _Compare = std::less<std::pair<long long int, long long int> >; _Alloc = std::allocator<std::pair<long long int, long long int> >]'
  569 |         { _M_t._M_insert_range_unique(__first, __last); }
      |           ~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~
a.cc:120:18:   required from here
  120 |         st.insert(a,b);
      |         ~~~~~~~~~^~~~~
/usr/include/c++/14/bits/stl_tree.h:1095:58: error: no type named 'value_type' in 'struct std::iterator_traits<long long int>'
 1095 |         __enable_if_t<__same_value_type<_InputIterator>::value>
      |                                                          ^~~~~
/usr/include/c++/14/bits/stl_set.h: In instantiation of 'void std::set<_Key, _Compare, _Alloc>::insert(_InputIterator, _InputIterator) [with _InputIterator = long long int; _Key = std::pair<long long int, long long int>; _Compare = std::less<std::pair<long long int, long long int> >; _Alloc = std::allocator<std::pair<long long int, long long int> >]':
a.cc:120:18:   required from here
  120 |         st.insert(a,b);
      |         ~~~~~~~~~^~~~~
/usr/include/c++/14/bits/stl_tree.h:1105:9: note: candidate: 'template<class _InputIterator> std::__enable_if_t<((bool)(! std::is_same<_Val, typename std::iterator_traits<_InputIterator>::value_type>::value))> std::_Rb_tree<_Key, _Val, _KeyOfValue, _Compare, _Alloc>::_M_insert_range_unique(_InputIterator, _InputIterator) [with _Key = std::pair<long long int, long long int>; _Val = std::pair<long long int, long long int>; _KeyOfValue = std::_Identity<std::pair<long long int, long long int> >; _Compare = std::less<std::pair<long long int, long long int> >; _Alloc = std::allocator<std::pair<long long int, long long int> >]'
 1105 |         _M_insert_range_unique(_InputIterator __first, _InputIterator __last)
      |         ^~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/14/bits/stl_tree.h:1105:9: note:   template argument deduction/substitution failed:
/usr/include/c++/14/bits/stl_tree.h: In substitution of 'template<class _InputIterator> std::__enable_if_t<((bool)(! std::is_same<std::pair<long long int, long long int>, typename std::iterator_traits< <template-parameter-1-1> >::value_type>::value)), void> std::_Rb_tree<std::pair<long long int, long long int>, std::pair<long long int, long long int>, std::_Identity<std::pair<long long int, long long int> >, std::less<std::pair<long long int, long long int> >, std::allocator<std::pair<long long int, long long int> > >::_M_insert_range_unique(_InputIterator, _InputIterator) [with _InputIterator = long long int]':
/usr/include/c++/14/bits/stl_set.h:569:31:   required from 'void std::set<_Key, _Compare, _Alloc>::insert(_InputIterator, _InputIterator) [with _InputIterator = long long int; _Key = std::pair<long long int, long long int>; _Compare = std::less<std::pair<long long int, long long int> >; _Alloc = std::allocator<std::pair<long long int, long long int> >]'
  569 |         { _M_t._M_insert_range_unique(__first, __last); }
      |           ~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~
a.cc:120:18:   required from here
  120 |         st.insert(a,b);
      |         ~~~~~~~~~^~~~~
/usr/include/c++/14/bits/stl_tree.h:1104:59: error: no type named 'value_type' in 'struct std::iterator_traits<long long int>'
 1104 |         __enable_if_t<!__same_value_type<_InputIterator>::value>
      |                                                           ^~~~~