How to Create Stack of Unordered Set in C++?

In C++, a stack is a container adapter that provides a Last-In-First-Out (LIFO) type of data structure, and an unordered set is a container that stores unique elements in no particular order. In this article, we will learn how to create a stack of unordered sets in C++.

Creating a Stack of Unordered Sets in C++

To create a std::stack of std::unordered_set, we can use the std::stack template class that takes the type of the elements as a template parameter. We can define this type as of unordered_set of a given type.

Syntax to Declare Stack of Unordered Set

stack<unordered_set<Type>> myStack

C++ Program to Create Stack of Unordered Set

C++

// C++ program to illustrate how to create a stack of
// unordered sets in C++
#include <iostream>
#include <stack>
#include <unordered_set>
using namespace std;

int main()
{
    // Declaring a stack of unordered sets
    stack<unordered_set<int> > myStack;

    // Creating some unordered sets
    unordered_set<int> set1 = { 1, 2, 3 };
    unordered_set<int> set2 = { 4, 5, 6 };
    unordered_set<int> set3 = { 7, 8, 9 };

    // Pushing unordered sets into the stack
    myStack.push(set1);
    myStack.push(set2);
    myStack.push(set3);

    // Checking if the stack is empty
    cout << "Stack Elements: " << endl;
    while (!myStack.empty()) {
        auto ele = myStack.top();
        int count = 1;
        cout << "uSet" << count << ": ";
        for (auto i : ele) {
            cout << i << " ";
        }
        count++;
        cout << endl;
        myStack.pop();
    }

    return 0;
}

Output

Stack Elements: 
uSet1: 9 7 8 
uSet1: 6 4 5 
uSet1: 3 1 2 

Time Complexity: O(N) where, N is the number of unordered sets.
Auxiliary Space: O(N)