如何在C ++中将键与映射的值交换？

给定一个映射，任务是用C++交换此映射的键及其值。

例子：

Input: map =
    {'e', 1 },
    {'o', 1 },
    {'r', 3 },
    
Output:
    {1, 'e' },
    {1, 'o' },
    {3, 'r' },

• 方法1：
  1. 通过使用向量对，遍历给定的地图
  2. push_back向量对中交换的值
  3. 将向量对按升序排序
  4. 在这种情况下，我们将无法获得STL映射功能，因为我们存储的结果是矢量对

  下面是上述方法的实现：

  // C++ program to swap keys
  // and values of a map
  // using Vector pair
    
  #include 
  using namespace std;
    
  // Function to swap keys and values of a map
  // and return a vector pair of the swapped values
  template 
  vector >
  invertMap2(map const& myMap)
  {
    
      vector > myvec;
    
      // traverse the map
      // and pushback the values -> keys
      for (auto const& pair : myMap) {
          myvec.push_back(
              make_pair(pair.second,
                        pair.first));
      }
    
      return myvec;
  }
    
  // Function to call the swap operation
  void swap(map char_frequency)
  {
    
      cout << "Original map:\n\n"
           << "KEY   Value\n";
      for (auto it
           = char_frequency.begin();
           it != char_frequency.end();
           ++it)
          cout << it->first << "   "
               << it->second << "\n";
    
      // create a vector pair of int, char
      // which store the swaped values
      vector > freq_char
          = invertMap2(char_frequency);
    
      // sort the vector pair to get
      // results similar to a map
      sort(freq_char.begin(),
           freq_char.end(),
           [](pair& a,
              pair& b) {
               if (a.first != b.first)
                   return a.first < b.first;
               return a.second < b.second;
           });
    
      cout << "\nMap with Keys and"
           << " Values swapped:\n\n"
           << "KEY   Value\n";
      for (auto it
           = freq_char.begin();
           it != freq_char.end();
           ++it)
          cout << it->first << "   "
               << it->second << "\n";
  }
    
  // Driver code
  int main()
  {
    
      // Taking the frequency map of
      // GeeksforGeeks as the input map here
      string input = "geeksforgeeks";
      map char_frequency;
      for (int i = 0; i < input.length(); ++i) {
          char_frequency[input[i]]++;
      }
    
      // Swap the keys with values of this map
      swap(char_frequency);
    
      return 0;
  }
  

  输出：

  Original map:
  
  KEY   Value
  e   4
  f   1
  g   2
  k   2
  o   1
  r   1
  s   2
  
  Map with Keys and Values swapped:
  
  KEY   Value
  1   f
  1   o
  1   r
  2   g
  2   k
  2   s
  4   e
  

• 方法2：另一种方法是使用STL MultiMap存储交换的地图，因为Map不能有重复的键。我们将遍历输入映射并将交换后的值插入到Multi-Map中。

  下面是上述方法的实现：

  // C++ program to swap keys
  // and values of a map
  // using STL MultiMap
    
  #include 
    
  using namespace std;
    
  // Function which swaps keys and
  // values of a map and
  // returns a multimap.
  template 
  multimap
  invertMap(map const& myMap)
  {
    
      multimap myMultiMap;
    
      // Traverse the map and
      // pushback the values -> keys
      for (auto const& pair : myMap) {
    
          myMultiMap.insert(
              make_pair(pair.second,
                        pair.first));
      }
      return myMultiMap;
  }
    
  // Function to call the swap operation
  void swap(map char_frequency)
  {
    
      cout << "Original map:\n\n"
           << "KEY   Value\n";
      for (auto it
           = char_frequency.begin();
           it != char_frequency.end();
           ++it)
          cout << it->first << "   "
               << it->second << "\n";
    
      // create a multimap of int, char
      multimap freq_char
          = invertMap(char_frequency);
    
      cout << "\nMap with Keys and"
           << " Values swapped:\n\n"
           << "KEY   Value\n";
      for (auto it
           = freq_char.begin();
           it != freq_char.end();
           ++it)
          cout << it->first << "   "
               << it->second << "\n";
  }
    
  // Driver code
  int main()
  {
    
      // Taking the frequency map of
      // GeeksforGeeks as the input map here
      string input = "geeksforgeeks";
      map char_frequency;
      for (int i = 0; i < input.length(); ++i) {
          char_frequency[input[i]]++;
      }
    
      // Swap the keys with values of this map
      swap(char_frequency);
    
      return 0;
  }
  

  输出：

  Original map:
  
  KEY   Value
  e   4
  f   1
  g   2
  k   2
  o   1
  r   1
  s   2
  
  Map with Keys and Values swapped:
  
  KEY   Value
  1   f
  1   o
  1   r
  2   g
  2   k
  2   s
  4   e
  

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