How To Delete Multiple Key-Value Pairs From Multimap in C++?

In C++, a multimap is a container that stores elements where each element has a key value and a mapped value. Unlike maps, multimaps allow multiple key-value pairs with the same key. In this article, we will learn how to delete multiple key-value pairs from a multimap in C++.

Example

Input: 
myMultimap = { {Student 1: 90}, {Student 1: 78}, {Student 2: 90},
                            {Student 3: 92}, {Student 4: 69} }
// deleting Student1 and Student2
Output:
myMultimap = { {Student 3: 92}, {Student 4: 69} }

Remove Multiple Key-Value Pairs From a Multimap

We can store the keys of the elements that we want to delete from the multimap in a vector. We can then iterate the vector and delete the elements associated with the keys using the std::multimap::erase() function.

C++ Program to Erase Multiple Key-Value Pairs from a Multimap

// C++ Program to show how to delete Multiple Key-Value
// pairs from the Multimap
#include <iostream>
#include <map>
#include <vector>

using namespace std;

int main()
{
    // Create a multimap
    multimap<int, string> myMultimap;
    myMultimap.insert(make_pair(1, "Apple"));
    myMultimap.insert(make_pair(2, "Banana"));
    myMultimap.insert(make_pair(1, "Mango"));
    myMultimap.insert(make_pair(3, "Peach"));
    myMultimap.insert(make_pair(2, "Grape"));

    // Create a vector to store keys of elements to be
    // deleted
    vector<int> keys = { 1, 2 };

    // Iterate over the vector and delete elements from the
    // multimap
    for (int key : keys) {
        myMultimap.erase(key);
    }

    // Print the remaining elements in the multimap
    for (auto it = myMultimap.begin();
         it != myMultimap.end(); ++it) {
        cout << it->first << " => " << it->second << '\n';
    }

    return 0;
}

3 => Peach

Time complexity: O(M log N), where N is the size of the multimap and M is the number of elements with the specified keys.
Space Complexity: O(M)