func_code_string: #include <bits/stdc++.h>   const double PI = 3.14159265358979323846;   using namespace std;   int main() {     std::map<int, long long> pairs;     std::set<long long> positive;     int n;     std::cin >> n;     std::vector<int> nums(n);     for (int i = 0; i < n; ++i) {       std::cin >> nums[i];       if (nums[i] > 0) {         positive.insert(nums[i]);       }       pairs[nums[i]]++;     }     long long result = 0;     if (pairs[0]) {       result += pairs[0] * (pairs[0] - 1) / 2;     }     for (std::set<long long>::iterator itr = positive.begin();          itr != positive.end(); ++itr) {       result += pairs[*itr] * pairs[-(*itr)];     }     std::cout << result << std::endl;     return 0;   }   