How to Create a Multimap of Vectors in C++?

In C++, a multimap is similar to a map with the addition that multiple elements can have the same keys. Also, it is not required that the key-value and mapped value pair have to be unique in this case. In this article, we will learn how to create a multimap of vectors in C++.

For Example,

Input:
myPair1 = {1, {2, 3, 4}}
myPair2 = {2, {5, 6, 7}}

Output:
MultiMap = { {1, {2, 3, 4}}, {2, {5, 6, 7}} }

Creating a Multimap of Vectors in C++

To create a multimap of vectors, we will have to first declare a multimap where in each key-value pair, the key is of type string and the value is a vector.

We can then use the std::multimap::insert() function to insert key-value pairs into the multimap. The key is a string, and the value is a vector.

Syntax to Create a Multimap of Vectors

 multimap<string, vector<int> > myMultimap;

C++ Program to Create a Multimap of Vectors

C++

// C++ program to create a multimap of vectors

#include <iostream>
#include <map>
#include <vector>
using namespace std;

int main()
{
    // Creating a multimap of string and vector
    multimap<string, vector<int> > myMultimap;

    // Inserting key-value pairs into the multimap
    myMultimap.insert({ "apple", { 1, 2 } });
    myMultimap.insert({ "banana", { 2, 3, 4 } });
    myMultimap.insert({ "cherry", { 3, 4, 5, 6 } });
    myMultimap.insert({ "apple", { 1, 2 } });

    // Displaying the multimap elements
    for (auto it = myMultimap.begin();
         it != myMultimap.end(); ++it) {
        cout << it->first << " ";
        for (auto vec_it = it->second.begin();
             vec_it != it->second.end(); ++vec_it) {
            cout << *vec_it << " ";
        }
        cout << endl;
    }

    return 0;
}

Output

apple 1 2 
apple 1 2 
banana 2 3 4 
cherry 3 4 5 6 

Time Complexity: O(N * log N), where N is the number of arrays.
Space Complexity: O(N * M), where M is the average size of the arrays.