unordered_set end() in C++ STL

The unordered_set::end() function is a built-in function in C++ STL which returns an iterator pointing to the past-the-end-element. This iterator does not directly point to an element, rather it points to the location just after the last element. Syntax

umap_name.end()

or,

umap_name.end(int i)

Parameters: This function takes a single integer parameter which is optional. Return value:

• If the parameter is not passed then the function returns an iterator pointing to the past-the-end element. Actually, it does not point to any element of the set, but it points to the position following the last element of the container.
• If the parameter is passed then the function returns an iterator pointing to the past-the-end element of i-th bucket. As in the previous case, it does not point to any element of the set, but it points to the position following the last element of i-th bucket. So the iterator returned by unordered_set::end() cannot be dereferenced.

Below programs illustrate the unordered_set::end() function: Program 1:

CPP

// CPP program to illustrate the unordered_set::end()
// function

#include <iostream>
#include <unordered_set>

using namespace std;

int main()
{
    unordered_set<int> sampleSet =
            { 5, 10, 15, 4, 2, 7, 8, 6 };

    // Continue the loop until it points to the
    // past-the-end position returned by sampleSet.end()
    for (auto it = sampleSet.begin(); it != sampleSet.end();
                                                        it++)
    {
        cout << *it << " ";
    }

    return 0;
}

Output:

6 8 7 2 4 15 10 5

Time Complexity: O(1)

Auxiliary Space: O(1)

Program 2: 

CPP

// CPP program to illustrate the
// unordered_set::end() function

#include <iostream>
#include <unordered_set>

using namespace std;

int main()
{
    unordered_set<int> sampleSet =
                { 5, 10, 15, 4, 2, 7, 8, 6 };

    // displaying all the buckets of the set.
    // Continue the loop until it points to the
    // past-the-end position returned by sampleset.end(i)
    for (unsigned i = 0; i < sampleSet.bucket_count(); ++i)
    {
        cout << "Bucket " << i << " Contains: ";
        for (auto it1 = sampleSet.begin(i);
                        it1 != sampleSet.end(i); ++it1)
            cout << " " << *it1;
        cout << endl;
    }

    return 0;
}

Output:

Bucket 0 Contains: 
Bucket 1 Contains: 
Bucket 2 Contains:  2
Bucket 3 Contains: 
Bucket 4 Contains:  4 15
Bucket 5 Contains:  5
Bucket 6 Contains:  6
Bucket 7 Contains:  7
Bucket 8 Contains:  8
Bucket 9 Contains: 
Bucket 10 Contains:  10

Time Complexity: O(1)

Auxiliary Space: O(1)