list erase() function in C++ STL

The list::erase() is a built-in function in C++ STL which is used to delete elements from a list container. This function can be used to remove a single element or a range of elements from the specified list container.

Syntax: 

iterator list_name.erase(iterator position)

or,

iterator list_name.erase(iterator first, iterator last)

Parameters: This function can accepts different parameters based on whether it is used to erase a single element or a range of element from the list container.

• position: This parameter is used when the function is used to delete a single element. This parameter refers to an iterator which points to the element which is need to be erased from the list container.
• first, last: These two parameters are used when the list is used to erase elements from a range. The parameter first refers to the iterator pointing to the first element in the range and the parameter last refers to the iterator pointing to the last element in the range which is needed to be erased. This erases all the elements in the range including the element pointed by the iterator first but excluding the element pointed by the iterator last.

Return Value: This function returns an iterator pointing to the element in the list container which followed the last element erased from the list container.

Below programs illustrates the list::erase() function.

Program 1: Erasing a single element. 

CPP

// CPP program to illustrate the
// list::erase() function
#include <bits/stdc++.h>
using namespace std;

int main()
{
    // Creating a list
    list<int> demoList;

    // Add elements to the List
    demoList.push_back(10);
    demoList.push_back(20);
    demoList.push_back(30);
    demoList.push_back(40);
    demoList.push_back(50);

    // Printing elements of list before deleting
    // first element
    cout << "List before deleting first element: ";
    for (auto itr = demoList.begin();
        itr != demoList.end(); itr++) {
        cout << *itr << " ";
    }

    // Creating iterator to point to first
    // element in the list
    list<int>::iterator itr = demoList.begin();

    // deleting the first element
    demoList.erase(itr);

    // Printing elements of list after deleting
    // first element
    cout << "\nList after deleting first element:";
    for (auto itr = demoList.begin();
        itr != demoList.end(); itr++) {
        cout << *itr << " ";
    }

    return 0;
}

Output

List before deleting first element: 10 20 30 40 50 
List after deleting first element:20 30 40 50

Time complexity: O(n) 
Space complexity: O(1)

Program 2: Erasing a range of elements. 

CPP

// CPP program to illustrate the
// list::erase() function
#include <bits/stdc++.h>
using namespace std;

int main()
{
    // Creating a list
    list<int> demoList;

    // Add elements to the List
    demoList.push_back(10);
    demoList.push_back(20);
    demoList.push_back(30);
    demoList.push_back(40);
    demoList.push_back(50);

    // Printing elements of list before deleting
    // any element
    cout << "List before deleting any element: ";
    for (auto itr = demoList.begin();
        itr != demoList.end(); itr++) {
        cout << *itr << " ";
    }

    // Creating iterators of the list
    list<int>::iterator itr1, itr2;
    itr1 = demoList.begin();
    itr2 = demoList.begin();

    // Incrementing itr2 by 3 positions
    advance(itr2, 3);

    // deleting range of elements from index [0, 3)
    demoList.erase(itr1, itr2);

    // Printing elements of list after deleting
    // range of elements from [0, 3)
    cout << "\nList after deleting first three elements: ";
    for (auto itr = demoList.begin();
        itr != demoList.end(); itr++) {
        cout << *itr << " ";
    }

    return 0;
}

Output

List before deleting any element: 10 20 30 40 50 
List after deleting first three elements: 40 50

Note: This function works in linear time complexity, that is the number of elements erased from the list container.

Time complexity: O(n) 
Space complexity: O(1)