What is the complexity indicator for adding an element to the beginning of a doubly linked list?

Adding an element to the beginning of a doubly linked list is performed in constant time, that is, it has a complexity of O(1).

This is because a doubly linked list has a pointer to the first element (head), and to insert a new element, it is enough to:

1. Create a new node.
2. Set its next pointer to the current first element.
3. Set the prev pointer of the current first element to the new node.
4. Update the head pointer of the list to the new node.

All these operations do not depend on the size of the list, so the complexity is — O(1).