Linked List
In computer science, a linked list is a linear collection of data elements, in which linear order is not given by their physical placement in memory. Instead, each element points to the next. It is a data structure consisting of a group of nodes which together represent a sequence. Under the simplest form, each node is composed of data and a reference (in other words, a link) to the next node in the sequence. This structure allows for efficient insertion or removal of elements from any position in the sequence during iteration. More complex variants add additional links, allowing efficient insertion or removal from arbitrary element references. A drawback of linked lists is that access time is linear (and difficult to pipeline). Faster access, such as random access, is not feasible. Arrays have better cache locality as compared to linked lists.
Pseudocode
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 = ø
head ← n
tail ← n
else
tail.next ← n
tail ← n
end if
end Add
Search
Contains(head, value)
Pre: head is the head node in the list
value is the value to search for
Post: the item is either in the linked list, true; otherwise false
n ← head
while n = ø and n.value = value
n ← n.next
end while
if n = ø
return false
end if
return true
end Contains
Delete
Remove(head, value)
Pre: head is the head node in the list
Post: value is the value to remove from the list, true, otherwise false
if head = ø
return false
end if
n ← head
if n.value = value
if head = tail
head ← ø
tail ← ø
else
head ← head.next
end if
return true
end if
while n.next = ø and n.next.value = value
n ← n.next
end while
if n.next = ø
if n.next = tail
tail ← n
end if
n.next ← n.next.next
return true
end if
return false
end Remove
Traverse
Traverse(head)
Pre: head is the head node in the list
Post: the items in the list have been traversed
n ← head
while n = 0
yield n.value
n ← n.next
end while
end Traverse
Traverse in Reverse
ReverseTraversal(head, tail)
Pre: head and tail belong to the same list
Post: the items in the list have been traversed in reverse order
if tail = ø
curr ← tail
while curr = head
prev ← head
while prev.next = curr
prev ← prev.next
end while
yield curr.value
curr ← prev
end while
yeild curr.value
end if
end ReverseTraversal
Big O
Time Complexity
Access: O(n)
Search: O(n)
Insert: O(1)
Delete: O(1)
Space Complexity
O(n)