Understanding Linked Lists
Linked lists consist of:
- Nodes: Each node contains data and a pointer to the next node.
- Head: Pointer to the first node in the list.
- Tail: The last node, which points to null.
Logical vs physical representation of linked lists:
- Logical Representation: How the list is viewed conceptually (nodes and pointers).
- Physical Representation: How the list is stored in memory (addresses and data types).
This distinction is an example of abstraction, hiding complex details to focus on essential features.
- Advantages of linked lists include:
- Dynamic Size: Can grow or shrink as needed.
- Efficient Insertions/Deletions: No need to shift elements, unlike arrays.
- Disadvantages of linked lists:
- Sequential Access: Must traverse the list to access elements.
- Memory Overhead: Each node requires extra memory for pointers.
Stacks, queues, and graphs can be built using linked lists.
Types of Linked Lists
Singly linked list: Each node points to the next node.
Doubly linked list: Each node points to both the next and previous nodes.
Doubly linked lists are ideal for applications that require frequent bidirectional traversal, such as navigation systems.
Circular linked list: The last node points back to the first node, forming a loop.
Circular linked lists are often used in operating systems for task scheduling, where each task is processed in a continuous loop.
Key Operations on Linked Lists
We can work with linked lists via:
- Insertion: Adding a new node.
- Deletion: Removing an existing node.
- Traversal: Visiting each node in sequence.
Linked lists are dynamic, meaning they can grow or shrink as needed, unlike arrays, which have a fixed size.
Insertion in a Linked List
- Create a new node: Allocate memory for the new node and set its data.
- Find the insertion point: Traverse the list to locate the node after which the new node will be inserted.
- Update Pointers:
- Set the new node's pointer to the next node.
- Update the previous node's (or head's if it is insertion at the beginning) pointer to the new node.
When inserting a node, always ensure that pointers are updated in the correct order to avoid breaking the list.
Deletion in a Linked List
- Find the Node to Delete: Traverse the list to locate the node.
- Update Pointers: Change the previous (or head's if it is deletion at the beginning) node's pointer to skip the node being deleted.
- Free Memory: Deallocate the memory used by the deleted node.
Traversing a Linked List
- Start at the Head: Begin with the first node.
- Follow Pointers: Move from one node to the next using pointers.
- End at Null: Stop when a node's pointer is null.
- Think of a linked list as a treasure hunt.
- Each node is a clue leading you to the next, until you reach the end.
Iterative example of traversing the linked list:
current_node = head
while current_node: # while it is not null
print(current_node.data)
current_node = current_node.next # move to the next node- While traversing, you can search for the value needed (compare nodes' values and traverse until found), as well as modify node's value.
- When modifying a node's data, ensure that the change does not violate any constraints, such as maintaining a sorted order.
Searching a linked list is a linear operation, with a time complexity of \$O(n)\$, where \$n\$ is the number of nodes.
- What are the key differences between linked lists and arrays?
- How does a linked list handle dynamic memory allocation?
- Why is it important to update pointers correctly during insertion and deletion?
How does the choice of data structure, such as linked lists versus arrays, reflect broader principles of efficiency and adaptability in computer science?
