Language: C++

#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;

inline bool suffice(int a, int b, int c)
{
  return
    a < b + c &&
    b < c + a &&
    c < a + b;
}

int main()
{
  int n;
  cin >> n;
  vector<int> list(n);
  for(int i = 0; i < n; ++i)
  {
    cin >> list[i];
  }
  
  sort(list.begin(), list.end());
  vector<int> skip(n, 1);
  {
    int pos = 0;
    while(pos < n)
    {
      int value = list[pos];
      int skip_count = 1;
      ++pos;
      while(pos < n && list[pos] == value) { ++skip_count; }
      skip[from] = skip_count;
    }
  }
  
  long long result = 0;
  auto end = list.end();
  for(auto i = list.begin(); i != end; i += skip[i])
  for(auto j = i + 1; j != end; j += skip[j])
  for(auto k = j + 1; k != end; k += skip[k])
  {
    if(suffice(*i, *j, *k))
    {
      result += skip[i] * skip[j] * skip[k];
    }
  }
  cout << result << endl;
  
  return 0;
}


Compiler output:
a.cc: In function 'int main()':
a.cc:34:12: error: 'from' was not declared in this scope
   34 |       skip[from] = skip_count;
      |            ^~~~
a.cc:40:49: error: no match for 'operator[]' (operand types are 'std::vector<int>' and '__gnu_cxx::__normal_iterator<int*, std::vector<int> >')
   40 |   for(auto i = list.begin(); i != end; i += skip[i])
      |                                                 ^
In file included from /usr/include/c++/14/vector:66,
                 from a.cc:2:
/usr/include/c++/14/bits/stl_vector.h:1128:7: note: candidate: 'std::vector<_Tp, _Alloc>::reference std::vector<_Tp, _Alloc>::operator[](size_type) [with _Tp = int; _Alloc = std::allocator<int>; reference = int&; size_type = long unsigned int]'
 1128 |       operator[](size_type __n) _GLIBCXX_NOEXCEPT
      |       ^~~~~~~~
/usr/include/c++/14/bits/stl_vector.h:1128:28: note:   no known conversion for argument 1 from '__gnu_cxx::__normal_iterator<int*, std::vector<int> >' to 'std::vector<int>::size_type' {aka 'long unsigned int'}
 1128 |       operator[](size_type __n) _GLIBCXX_NOEXCEPT
      |                  ~~~~~~~~~~^~~
/usr/include/c++/14/bits/stl_vector.h:1147:7: note: candidate: 'std::vector<_Tp, _Alloc>::const_reference std::vector<_Tp, _Alloc>::operator[](size_type) const [with _Tp = int; _Alloc = std::allocator<int>; const_reference = const int&; size_type = long unsigned int]'
 1147 |       operator[](size_type __n) const _GLIBCXX_NOEXCEPT
      |       ^~~~~~~~
/usr/include/c++/14/bits/stl_vector.h:1147:28: note:   no known conversion for argument 1 from '__gnu_cxx::__normal_iterator<int*, std::vector<int> >' to 'std::vector<int>::size_type' {aka 'long unsigned int'}
 1147 |       operator[](size_type __n) const _GLIBCXX_NOEXCEPT
      |                  ~~~~~~~~~~^~~
a.cc:41:42: error: no match for 'operator[]' (operand types are 'std::vector<int>' and '__gnu_cxx::__normal_iterator<int*, std::vector<int> >')
   41 |   for(auto j = i + 1; j != end; j += skip[j])
      |                                          ^
/usr/include/c++/14/bits/stl_vector.h:1128:7: note: candidate: 'std::vector<_Tp, _Alloc>::reference std::vector<_Tp, _Alloc>::operator[](size_type) [with _Tp = int; _Alloc = std::allocator<int>; reference = int&; size_type = long unsigned int]'
 1128 |       operator[](size_type __n) _GLIBCXX_NOEXCEPT
      |       ^~~~~~~~
/usr/include/c++/14/bits/stl_vector.h:1128:28: note:   no known conversion for argument 1 from '__gnu_cxx::__normal_iterator<int*, std::vector<int> >' to 'std::vector<int>::size_type' {aka 'long unsigned int'}
 1128 |       operator[](size_type __n) _GLIBCXX_NOEXCEPT
      |                  ~~~~~~~~~~^~~
/usr/include/c++/14/bits/stl_vector.h:1147:7: note: candidate: 'std::vector<_Tp, _Alloc>::const_reference std::vector<_Tp, _Alloc>::operator[](size_type) const [with _Tp = int; _Alloc = std::allocator<int>; const_reference = const int&; size_type = long unsigned int]'
 1147 |       operator[](size_type __n) const _GLIBCXX_NOEXCEPT
      |       ^~~~~~~~
/usr/include/c++/14/bits/stl_vector.h:1147:28: note:   no known conversion for argument 1 from '__gnu_cxx::__normal_iterator<int*, std::vector<int> >' to 'std::vector<int>::size_type' {aka 'long unsigned int'}
 1147 |       operator[](size_type __n) const _GLIBCXX_NOEXCEPT
      |                  ~~~~~~~~~~^~~
a.cc:42:42: error: no match for 'operator[]' (operand types are 'std::vector<int>' and '__gnu_cxx::__normal_iterator<int*, std::vector<int> >')
   42 |   for(auto k = j + 1; k != end; k += skip[k])
      |                                          ^
/usr/include/c++/14/bits/stl_vector.h:1128:7: note: candidate: 'std::vector<_Tp, _Alloc>::reference std::vector<_Tp, _Alloc>::operator[](size_type) [with _Tp = int; _Alloc = std::allocator<int>; reference = int&; size_type = long unsigned int]'
 1128 |       operator[](size_type __n) _GLIBCXX_NOEXCEPT
      |       ^~~~~~~~
/usr/include/c++/14/bits/stl_vector.h:1128:28: note:   no known conversion for argument 1 from '__gnu_cxx::__normal_iterator<int*, std::vector<int> >' to 'std::vector<int>::size_type' {aka 'long unsigned int'}
 1128 |       operator[](size_type __n) _GLIBCXX_NOEXCEPT
      |                  ~~~~~~~~~~^~~
/usr/include/c++/14/bits/stl_vector.h:1147:7: note: candidate: 'std::vector<_Tp, _Alloc>::const_reference std::vector<_Tp, _Alloc>::operator[](size_type) const [with _Tp = int; _Alloc = std::allocator<int>; const_reference = const int&; size_type = long unsigned int]'
 1147 |       operator[](size_type __n) const _GLIBCXX_NOEXCEPT
      |       ^~~~~~~~
/usr/include/c++/14/bits/stl_vector.h:1147:28: note:   no known conversion for argument 1 from '__gnu_cxx::__normal_iterator<int*, std::vector<int> >' to 'std::vector<int>::size_type' {aka 'long unsigned int'}
 1147 |       operator[](size_type __n) const _GLIBCXX_NOEXCEPT
      |                  ~~~~~~~~~~^~~
a.cc:46:21: error: no match for 'operator[]' (operand types are 'std::vector<int>' and '__gnu_cxx::__normal_iterator<int*, std::vector<int> >')
   46 |       result += skip[i] * skip[j] * skip[k];
      |                     ^
/usr/include/c++/14/bits/stl_vector.h:1128:7: note: candidate: 'std::vector<_Tp, _Alloc>::reference std::vector<_Tp, _Alloc>::operator[](size_type) [with _Tp = int; _Alloc = std::allocator<int>; reference = int&; size_type = long unsigned int]'
 1128 |       operator[](size_type __n) _GLIBCXX_NOEXCEPT
      |       ^~~~~~~~
/usr/include/c++/14/bits/stl_vector.h:1128:28: note:   no known conversion for argument 1 from '__gnu_cxx::__normal_iterator<int*, std::vector<int> >' to 'std::vector<int>::size_type' {aka 'long unsigned int'}
 1128 |       operator[](size_type __n) _GLIBCXX_NOEXCEPT
      |                  ~~~~~~~~~~^~~
/usr/include/c++/14/bits/stl_vector.h:1147:7: note: candidate: 'std::vector<_Tp, _Alloc>::const_reference std::vector<_Tp, _Alloc>::operator[](size_type) const [with _Tp = int; _Alloc = std::allocator<int>; const_reference = const int&; size_type = long unsigned int]'
 1147 |       operator[](size_type __n) const _GLIBCXX_NOEXCEPT
      |       ^~~~~~~~
/usr/include/c++/14/bits/stl_vector.h:1147:28: note:   no known conversion for argument 1 from '__gnu_cxx::__normal_iterator<int*, std::vector<int> >' to 'std::vector<int>::size_type' {aka 'long unsigned int'}
 1147 |       operator[](size_type __n) const _GLIBCXX_NOEXCEPT
      |                  ~~~~~~~~~~^~~
a.cc:46:31: error: no match for 'operator[]' (operand types are 'std::vector<int>' and '__gnu_cxx::__normal_iterator<int*, std::vector<int> >')
   46 |       result += skip[i] * skip[j] * skip[k];
      |                               ^
/usr/include/c++/14/bits/stl_vector.h:1128:7: note: candidate: 'std::vector<_Tp, _Alloc>::reference std::vector<_Tp, _Alloc>::operator[](size_type) [with _Tp = int; _Alloc = std::allocator<int>; reference = int&; size_type = long unsigned int]'
 1128 |       operator[](size_type __n) _GLIBCXX_NOEXCEPT
      |       ^~~~~~~~
/usr/include/c++/14/bits/stl_vector.h:1128:28: note:   no known conversion for argument 1 from '__gnu_cxx::__normal_iterator<int*, std::vector<int> >' to 'std::vector<int>::size_type' {aka 'long unsigned int'}
 1128 |       operator[](size_type __n) _GLIBCXX_NOEXCEPT
      |                  ~~~~~~~~~~^~~
/usr/include/c++/14/bits/stl_vector.h:1147:7: note: candidate: 'std::vector<_Tp, _Alloc>::const_reference std::vector<_Tp, _Alloc>::operator[](size_type) const [with _Tp = int; _Alloc = std::allocator<int>; const_reference = const int&; size_type = long unsigned int]'
 1147 |       operator[](size_type __n) const _GLIBCXX_NOEXCEPT
      |       ^~~~~~~~
/usr/include/c++/14/bits/stl_vector.h:1147:28: note:   no known conversion for argument 1 from '__gnu_cxx::__normal_iterator<int*, std::vector<int> >' to 'std::vector<int>::size_type' {aka 'long unsigned int'}
 1147 |       operator[](size_type __n) const _GLIBCXX_NOEXCEPT
      |                  ~~~~~~~~~~^~~
a.cc:46:41: error: no match for 'operator[]' (operand types are 'std::vector<int>' and '__gnu_cxx::__normal_iterator<int*, std::vector<int> >')
   46 |       result += skip[i] * skip[j] * skip[k];
      |                                         ^
/usr/include/c++/14/bits/stl_vector.h:1128:7: note: candidate: 'std::vector<_Tp, _Alloc>::reference std::vector<_Tp, _Alloc>::operator[](size_type) [with _Tp = int; _Alloc = std::allocator<int>; reference = int&; size_type = long unsigned int]'
 1128 |       operator[](size_type __n) _GLIBCXX_NOEXCEPT
      |       ^~~~~~~~
/usr/include/c++/14/bits/stl_vector.h:1128:28: note:   no known conversion for argument 1 from '__gnu_cxx::__normal_iterator<int*, std::vector<int> >' to 'std::vector<int>::size_type' {aka 'long unsigned int'}
 1128 |       operator[](size_type __n) _GLIBCXX_NOEXCEPT
      |                  ~~~~~~~~~~^~~
/usr/include/c++/14/bits/stl_vector.h:1147:7: note: candidate: 'std::vector<_Tp, _Alloc>::const_reference std::vector<_Tp, _Alloc>::operator[](size_type) const [with _Tp = int; _Alloc = std::allocator<int>; const_reference = const int&; size_type = long unsigned int]'
 1147 |       operator[](size_type __n) const _GLIBCXX_NOEXCEPT
      |       ^~~~~~~~
/usr/include/c++/14/bits/stl_vector.h:1147:28: note:   no known conversion for argument 1 from '__gnu_cxx::__normal_iterator<int*, std::vector<int> >' to 'std::vector<int>::size_type' {aka 'long unsigned int'}
 1147 |       operator[](size_type __n) const _GLIBCXX_NOEXCEPT
      |                  ~~~~~~~~~~^~~