list insert() in C++ STL

The list::insert() is used to insert the elements at any position of list. This function takes 3 elements, position, number of elements to insert and value to insert. If not mentioned, number of elements is default set to 1. Syntax:

insert(pos_iter, ele_num, ele)

Parameters: This function takes in three parameters:

• pos_iter: Position in the container where the new elements are inserted.
• ele_num: Number of elements to insert. Each element is initialized to a copy of val.
• ele: Value to be copied (or moved) to the inserted elements.

Return Value: This function returns an iterator that points to the first of the newly inserted elements. 

CPP

// C++ code to demonstrate the working of
// insert() function

#include <iostream>
#include <list> // for list operations
using namespace std;

int main()
{
    // declaring list
    list<int> list1;

    // using assign() to insert multiple numbers
    // creates 3 occurrences of "2"
    list1.assign(3, 2);

    // initializing list iterator to beginning
    list<int>::iterator it = list1.begin();

    // iterator to point to 3rd position
    advance(it, 2);

    // using insert to insert 1 element at the 3rd position
    // inserts 5 at 3rd position
    list1.insert(it, 5);

    // Printing the new list
    cout << "The list after inserting"
         << " 1 element using insert() is : ";
    for (list<int>::iterator i = list1.begin();
         i != list1.end();
         i++)
        cout << *i << " ";

    cout << endl;

    // using insert to insert
    // 2 element at the 4th position
    // inserts 2 occurrences
    // of 7 at 4th position
    list1.insert(it, 2, 7);

    // Printing the new list
    cout << "The list after inserting"
         << " multiple elements "
         << "using insert() is : ";

    for (list<int>::iterator i = list1.begin();
         i != list1.end();
         i++)
        cout << *i << " ";

    cout << endl;
}

Output:

The list after inserting 1 element using insert() is : 2 2 5 2 
The list after inserting multiple elements using insert() is : 2 2 5 7 7 2

Time Complexity – Linear O(N)