std::list

Learn doubly linked lists with std::list.

std::list

std::list is a doubly linked list. push_front adds to the beginning, push_back to the end. front() returns the first element.

Example: std::list<int> l; l.push_front(10); l.push_front(20);. Now the list is 20 -> 10. l.front() returns 20. Because push_front adds at the head, the last added element is first. A linked list does O(1) insert/erase in the middle.

list vs vector

list offers O(1) insert/erase in the middle (given an iterator). But there is NO random access: l[2] won't compile. Sequential access uses iterators.

vector offers O(1) random access (v[2]), but middle insertion is O(n). Choose: frequent middle inserts need list; frequent random access needs vector. Memory: vector is contiguous; list is node-by-node with overhead.

Exercise Work with list

Create std::list<int> l;. Call push_front(10) then push_front(20). Print l.front() with std::cout.

Show example solution

#include <iostream>
#include <list>

int main() {
    std::list<int> l;
    l.push_front(10);
    l.push_front(20);
    std::cout << l.front() << std::endl;
    return 0;
}

Test yourself

Complete the push_front call
```
l.push_front(____);
```
Show answer
```
l.push_front(10);
```
Which operation is NOT possible on a list?
```
std::list<int> l;
```
- push_front
- push_back
- front()
- access with l[2]
Show answer

access with l[2] — list has no random access; l[2] won't compile.
Match method to role

push_front

Add to head
push_back

Add to tail
front()

First element
size()

Element count

Next lesson: std::map

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