Multimap stores key-value pairs and for the same key, we can have more than one value i.e. multiple values for a single key. We can use this property of multimap to group vector of pair elements easily. In this article, we will discuss how to group elements of a vector of pairs in a multimap container.

Example

Input:
myVector ={ {"A", 80},{"B", 70},{"A", 90},{"C", 90},{"B", 60},{"A", 100}}

Output:
myMultiMap = { {"A", 80},{"A", 90},{"A", 100},{"B", 60},{"B", 70},{"C", 90}}

Grouping of Vector of Pair Elements

We can just create a multimap of the same type as a pair and insert the vector elements in the map using the insert function. After that, we can access all the key-value pairs with the same key using the std::multimap::equal_range() function.

C++ Program to Group Vector of Pairs Elements in a Multimap

Output

All Key-Value pairs:
Key: 1
  Value: Apple
  Value: Apricot
Key: 1
  Value: Apple
  Value: Apricot
Key: 2
  Value: Banana
  Value: Blueberry
Key: 2
  Value: Banana
  Value: Blueberry
Key: 3
  Value: Cherry

Time Complexity: O(N log(N))
Auxiliary Space: O(N)