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  1. #include <bits/stdc++.h>
  2.  
  3. using namespace std;
  4. int cal(string fomulas){
  5.     unordered_map <char, int> atomic {
  6.         {'H',1},
  7.         {'C',12},
  8.         {'N',14},
  9.         {'O',16}
  10.     };
  11.     regex molecule ("([HCNO])(\\d*)");
  12.     smatch match;
  13.     int weight = 0;
  14.     string remain = fomulas;
  15.     while (regex_search (remain, match, molecule)){
  16.         char element = match[1].str()[0];
  17.         int count = 1;
  18.         if (!match[2].str().empty()) count = stoi (match[2].str());
  19.         weight += atomic[element] * count;
  20.         remain = match.suffix().str();
  21.     }
  22.     return weight;
  23. }
  24. int main() {
  25.     ios_base::sync_with_stdio(false);
  26.     cin.tie(NULL);
  27.     string fomulas;
  28.     cin >> fomulas;
  29.     cout << cal(fomulas);
  30.     return 0;
  31. }
Success #stdin #stdout 0.01s 5548KB
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stdin
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C2H4
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https://ideone.com/NeoHYJ
language:
C++ (gcc 8.3)
created:
2 years ago
visibility:
public

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