set insert() function in C++ STL

The set::insert is a built-in function in C++ STL which insert elements in the set container or inserts the elements from a position to another position in the set to a different set.

• Syntax: 

iterator set_name.insert(element)

Parameters: The function accepts a mandatory parameter element which is to be inserted in the set container. 
Return Value: The function returns a pair of type pair<iterator, bool>, where

• pair::first is an iterator that points to the newly inserted element or to the same element already in the set.
• pair::second is a boolean value that is set to true if a new element was inserted or false if the same element already exists.

Time Complexity: log(N) Where ‘N’ is the number of elements in the set 
Below program illustrates the above function: 

CPP

// CPP program to demonstrate the
// set::insert(element) function
#include <bits/stdc++.h>
using namespace std;
int main()
{

    set<int> s;

    // Function to insert elements
    // in the set container
    s.insert(1);
    s.insert(4);
    s.insert(2);
    s.insert(5);
    s.insert(3);

    cout << "The elements in set are: ";
    for (auto it = s.begin(); it != s.end(); it++)
        cout << *it << " ";

    return 0;
}

Output

The elements in set are: 1 2 3 4 5

• Syntax: 

iterator set_name.insert(iterator position, element)

Parameters: The function accepts two parameter which are described below: 

• element: It specifies the element to be inserted in the set container.
• position: It does not specify the position where the insertion is to be done, it only points to a position from where the searching operation is to be started for insertion to make the process faster. The insertion is done according to the order which is followed by the set container.
• Syntax: 

void set_name.insert(iterator position1, iterator position2)

Parameters: The function accepts two parameters position1 and position2 which specifies the range of elements. All the elements in the range [position1, last) are inserted in another set container. 
Return Value: No return type => void. 
Below program illustrates the above function: 

CPP

// CPP program to demonstrate the
// set::insert(iterator1, iterator2) function
#include <bits/stdc++.h>
using namespace std;
int main()
{

    set<int> s1;

    // Function to insert elements
    // in the set container
    s1.insert(1);
    s1.insert(4);
    s1.insert(2);
    s1.insert(5);
    s1.insert(3);

    cout << "The elements in set1 are: ";
    for (auto it = s1.begin(); it != s1.end(); it++)
        cout << *it << " ";

    set<int> s2;

    // Function to insert one set to another
    // all elements from where 3 is to end is
    // inserted to set2
    s2.insert(s1.find(3), s1.end());

    cout << "\nThe elements in set2 are: ";
    for (auto it = s2.begin(); it != s2.end(); it++)
        cout << *it << " ";

    return 0;
}

Output

The elements in set1 are: 1 2 3 4 5 
The elements in set2 are: 3 4 5