unordered_set begin() in C++

begin(): This function is available in the File: unordered_set.h.

Syntax:

std::unordered_set<int>::iterator std::unordered_set<int>::begin()

This function returns a read-only (constant) iterator that points to the first element in the unordered_set.

Parameters: This functions takes one argument (or no argument).

File: unordered_set.h

For Example:

st = {9,4}

unordered_set<int>::iterator it = st.begin() => It points to the first-iterator (i.e 4).

Approach 1: When the function does not take any argument.

C++

#include <bits/stdc++.h>
using namespace std;

int main()
{
    unordered_set<int> st;
    st.insert(9);
    st.insert(4);

    unordered_set<int>::iterator it = st.begin();

    cout << *it << "\n";

    return 0;
}

Output:

4

Approach 2: When the functions take an argument.

C++

#include <bits/stdc++.h>
using namespace std;

int main()
{
    unordered_set<int> st = {9, 4, 10, 12, 3, 4, 15};

    for (int i = 0; i < st.bucket_count(); i++)
    {
        cout << "Bucket " << i << " contains: ";
        for (auto it = st.begin(i); it != st.end(i); it++)
            cout << *it << " ";

        cout << "\n";
    }

    return 0;
}

Output:

Bucket 0 contains: 
Bucket 1 contains: 12
Bucket 2 contains:
Bucket 3 contains: 3
Bucket 4 contains: 15 4
Bucket 5 contains:
Bucket 6 contains:
Bucket 7 contains:
Bucket 8 contains: 
Bucket 9 contains: 9
Bucket 10 contains: 10