Doubly Linked List
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In computer science, a doubly linked list is a linked data structure that consists of a set of sequentially linked records called nodes. Each node contains two fields, called links, that are references to the previous and to the next node in the sequence of nodes. The beginning and ending nodes' previous and next links, respectively, point to some kind of terminator, typically a sentinel node or null, to facilitate the traversal of the list. If there is only one sentinel node, then the list is circularly linked via the sentinel node. It can be conceptualized as two singly linked lists formed from the same data items, but in opposite sequential orders.
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The two node links allow traversal of the list in either direction. 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.
Pseudocode for Basic Operations
Insert
Add(value)
Pre: value is the value to add to the list
Post: value has been placed at the tail of the list
n - node(value)
if head = o
head - n
tail - n
else
n.previous - tail
tail.next - n
tail - n
end if
end Add
Delete
Remove(head, value)
Pre: head is the head node in the list
value is the value to remove from the list
Post: value is removed from the list, true; otherwise false
if head = o
return false
end if
if value = head.value
if head = tail
head - o
tail - o
else
head - head.next
head.previous - o
end if
return true
end if
n - head.next
while n != o and value !== n.value
n - n.next
end while
if n = tail
tail - tail.previous
tail.next - o
return true
else if n != o
n.previous.next - n.next
n.next.previous - n.previous
return true
end if
return false
end Remove
Reverse Traversal
ReverseTraversal(tail)
Pre: tail is the node of the list to traverse
Post: the list has been traversed in reverse order
n - tail
while n != o
yield n.value
n - n.previous
end while
end Reverse Traversal
Complexities
Time Complexity
| Access | Search | Insertion | Deletion |
|---|---|---|---|
| O(n) | O(n) | O(1) | O(n) |
Space Complexity
O(n)