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

In C++, Stacks are a type of container adaptor with LIFO(Last In First Out) type of working, where a new element is added at one end (top) and an element is removed from that end only. A multimap is a container that stores key-value pairs in an ordered manner. In this article, we will learn how to create a stack of multimaps in C++.

Example:

Input: 
myMultimap1 =  { {1, “C++”}, {2, “Java”}, {1, “Python”} };
myMultimap2 =  { {2, “JavaScript”} };
Output: 
myStack: [ { {1, “C++”}, {2, “Java”}, {1, “Python”} },
                    { {2, “JavaScript”} } ]

Stack of Multimaps in C++

To create a stack of multimaps in C++, we have to define the type of stack elements as a multimap in the template definition. The stack can store any type of data, including complex data types like multimaps.

Syntax to Declare Stack of Multimap

stack < multimap <keyType, valueType> myStack;

C++ Program to Create a Stack of Multimaps

// C++ Program to illustrate how to create a stack of
// multimaps
#include <iostream>
#include <map>
#include <stack>
using namespace std;

int main()
{
    // Initialize a multimap with some entries
    multimap<int, string> myMultimap1
        = { { 1, "C++" }, { 2, "Java" } };
    multimap<int, string> myMultimap2
        = { { 1, "Python" }, { 2, "JavaScript" } };

    // Create a stack of multimaps
    stack<multimap<int, string> > myStack;
    myStack.push(myMultimap1);
    myStack.push(myMultimap2);

    // Print multimap in the stack
    cout << "myStack:" << endl << "[";
    while (!myStack.empty()) {
        auto ele = myStack.top();
        cout << " { ";
        for (auto& pair : ele) {
            cout << "{" << pair.first << ", " << pair.second
                 << "}, ";
        }
        cout << " } ";
        myStack.pop();
    }
    cout << " ]";

    return 0;
}

myStack:
[ { {1, Python}, {2, JavaScript},  }  { {1, C++}, {2, Java},  } ]

Time Complexity: O(N) where n is the number of multimaps.
Auxiliary Space: O(N * M), where M is the average size of the multimaps.