unordered_set size() function in C++ STL

The unordered_set::size() method is a builtin function in C++ STL which is used to return the number of elements in the unordered_set container.

Syntax:

unordered_set_name.size()

Parameter: It does not accepts any parameter.

Return Value: The function returns the number of elements in the container. Below programs illustrate the unordered_set::size() function:

Program 1:

CPP

// C++ program to illustrate the 
// unordered_set.size() function 
#include <iostream> 
#include <unordered_set> 

using namespace std; 

int main() 
{ 

    unordered_set<int> arr1 = { 1, 2, 3, 4, 5 }; 

    // prints the size of arr1 
    cout << "size of arr1:" << arr1.size(); 

    // prints the element 
    cout << "\nThe elements are: "; 
    for (auto it = arr1.begin(); it != arr1.end(); it++) 
        cout << *it << " "; 

    return 0; 
}

Output:

size of arr1:5
The elements are: 5 1 2 3 4

Program 2:

CPP

// C++ program to illustrate the 
// unordered_set::size() function 
// when container is empty 
#include <iostream> 
#include <unordered_set> 

using namespace std; 

int main() 
{ 

    unordered_set<int> arr2 = {}; 

    // prints the size 
    cout << "Size of arr2 : " << arr2.size(); 

    return 0; 
}

Output:

Size of arr2 : 0

Time complexity: O(1)

unordered_set size() function in C++ STL

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