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  1.  
  2. #include <iostream>
  3. #include <vector>
  4. #include <string>
  5. #include <unordered_map>
  6.  
  7. template<typename T>
  8. class lookup {
  9.   std::unordered_map<T, int> position;
  10. public:
  11.   lookup(const std::vector<T>& a) {
  12.     for(int i = 0; i < a.size(); ++i) position.emplace(a[i], i);
  13.   }
  14.   int operator()(const T& key) const {
  15.     auto pos = position.find(key);
  16.     return pos == position.end() ? -1 : pos->second;
  17.   }
  18. };
  19.  
  20. template<typename T>
  21. static lookup<T> make_lookup(const std::vector<T>& a) {
  22.   return lookup<T>(a);
  23. }
  24.  
  25. int main() {
  26.   std::vector<std::string> foo{"a", "b", "d", "e", "g", "k", "m", "n", "r", "x"};
  27.   auto find = make_lookup(foo);
  28.   for(std::string key : {"g", "m", "p"}) {
  29.     std::cout << find(key) << std::endl;
  30.   }
  31.   return 0;
  32. }
  33.  
  34.  
Success #stdin #stdout 0s 3416KB
comments (?)
stdin 
Standard input is empty
stdout 
4
6
-1
https://ideone.com/2FyMUx
language:
C++14 (gcc 8.3)
created:
9 years ago
visibility:
public

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