Image : Doubly-linked-list . svg " A doubly linked list whose nodes contain three fields : an integer value, the link forward to the next node, and the link backward to the previous node"
22.
In the case of a circular doubly linked list, the only change that occurs is that the end, or " tail ", of the said list is linked back to the front, or " head ", of the list and vice versa.
23.
Notice that we also don't need separate " removeBefore " or " removeAfter " methods, because in a doubly linked list we can just use " remove ( node . prev ) " or " remove ( node . next ) " where these are valid.
24.
Some architectures provide " larger " atomic operations such that, as example, both forward and backward links in a doubly linked list can be updated atomically ( this in fact only applies to the Motorola 68k family, the most recent version being released in 1994 ).
25.
While adding or removing a node in a doubly linked list requires changing more links than the same operations on a singly linked list, the operations are simpler and potentially more efficient ( for nodes other than first nodes ) because there is no need to keep track of the previous node during traversal or no need to traverse the list to find the previous node, so that its link can be modified.
26.
When Algorithm X is implemented efficiently using Donald Knuth's Dancing Links technique on a computer, Knuth calls it DLX . DLX uses the matrix representation of the problem, implemented as a series of doubly linked lists of the 1s of the matrix : each 1 element has a link to the next 1 above, below, to the left, and to the right of itself . ( Technically, because the lists are circular, this forms a torus ).
27.
But neither, to be pedantic ( which is all what language and library standards are about ) does it explicitly say ( that I can find ) that references etc . are valid until the item is explicitly destroyed-it would be bonkers if they were invalidated somehow, and the standard very strongly implies that the implementation will be a doubly linked list of items ( e . g . list . insert insists that this be a constant time operation, whereas vector . insert does not ).
