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  1. #include <set>
  2. #include <utility>
  3. #include <iostream>
  4. #include <algorithm>
  5.  
  6. using std::make_pair;
  7.  
  8. template<typename X, typename Y, typename Xless = std::less<X>, typename Yless = std::less<Y>>
  9. class bimap
  10. {
  11.     typedef std::pair<X, Y>                             key_type;
  12.     typedef std::pair<X, Y>                             value_type;
  13.     typedef typename std::set<key_type>::iterator       iterator;
  14.     typedef typename std::set<key_type>::const_iterator const_iterator;
  15.  
  16.     struct Xcomp
  17.     {
  18.         bool operator()(X const &x1, X const &x2)
  19.         {
  20.             return !Xless()(x1, x2) && !Xless()(x2, x1);
  21.         }
  22.     };
  23.     struct Ycomp
  24.     {
  25.         bool operator()(Y const &y1, Y const &y2)
  26.         {
  27.             return !Yless()(y1, y2) && !Yless()(y2, y1);
  28.         }
  29.     };
  30.     struct Fless 
  31.     { // prevents lexicographical comparison for std::pair, so that 
  32.         // every .first value is unique as if it was in its own map
  33.         bool operator()(key_type const &lhs, key_type const &rhs)
  34.         {
  35.             return Xless()(lhs.first, rhs.first);
  36.         }
  37.     };
  38.     /// key and value type are interchangeable
  39.     std::set<std::pair<X, Y>, Fless> _data;
  40.  
  41. public:
  42.     std::pair<iterator, bool> insert(X const &x, Y const &y)
  43.     {
  44.         auto it = find_right(y);
  45.         if (it == end()) { // every .second value is unique
  46.             return _data.insert(make_pair(x, y));
  47.         }
  48.         return make_pair(it, false);
  49.     }
  50.     iterator find_left(X const &val)
  51.     {
  52.         return _data.find(make_pair(val,Y()));
  53.     }
  54.     iterator find_right(Y const &val)
  55.     {
  56.         return std::find_if(_data.begin(), _data.end(), 
  57.             [&val](key_type const &kt)
  58.         {
  59.             return Ycomp()(kt.second, val);
  60.         });
  61.     }
  62.     iterator end()   { return _data.end();   }
  63.     iterator begin() { return _data.begin(); }
  64. };
  65.  
  66. template<typename X, typename Y, typename In>
  67. void PrintBimapInsertion(X const &x, Y const &y, In const &in)
  68. {
  69.     if (in.second) {
  70.         std::cout << "Inserted element (" 
  71.             << in.first->first << ", " << in.first->second << ")\n";
  72.     }
  73.     else {
  74.         std::cout << "Could not insert (" << x << ", " << y << ") because (" << 
  75.             in.first->first << ", " << in.first->second << ") already exists\n";
  76.     }
  77. }
  78.  
  79.  
  80. int main()
  81. {
  82.     bimap<std::string, int> mb;
  83.     PrintBimapInsertion("A", 1, mb.insert("A", 1) );
  84.     PrintBimapInsertion("A", 2, mb.insert("A", 2) );
  85.     PrintBimapInsertion("b", 2, mb.insert("b", 2));
  86.     PrintBimapInsertion("z", 2, mb.insert("z", 2));
  87.  
  88.     auto it1 = mb.find_left("A");
  89.     if (it1 != mb.end()) {
  90.         std::cout << std::endl << it1->first << ", " << it1->second << std::endl;
  91.     }
  92.  
  93.     auto it2 = mb.find_right(2);
  94.     if (it2 != mb.end()) {
  95.         std::cout << std::endl << it2->first << ", " << it2->second << std::endl;
  96.     }
  97.  
  98.     return 0;
  99. }
Success #stdin #stdout 0s 3476KB
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stdin
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Standard input is empty
stdout
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Inserted element (A, 1)
Could not insert (A, 2) because (A, 1) already exists
Inserted element (b, 2)
Could not insert (z, 2) because (b, 2) already exists

A, 1

b, 2
https://ideone.com/ygBbYn
language:
C++14 (gcc 8.3)
created:
10 years ago
visibility:
public

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