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unordered_set end() in C++ STL

Last Updated : 05 Jun, 2023

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  i    which is optional. 

Return value:

• If the parameter  i    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  i    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 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; 
} 

6 8 7 2 4 15 10 5

Time Complexity: O(1)

Auxiliary Space: O(1)

Program 2: 

// 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; 
} 

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)

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