Remove Linked List Elements
To remove all the nodes with a specific value from a linked list, we can use a twopointer approach: one to keep track of the current node and another to keep track of the previous node. By doing this, we can change the pointers of the nodes to skip over nodes with the value we want to remove.
Here’s the code:


Explanation:
 We create a dummy node to simplify the handling of the edge case where the head node needs to be removed.
 We use two pointers,
prev
andcurr
, to traverse the list.  If the current node’s value equals the target value, we change the previous node’s next pointer to the current node’s next pointer, effectively skipping over the current node and removing it.
 If the current node’s value does not equal the target value, we move the previous pointer to the current node.
 Finally, we return the new head, which is the next node of the dummy.
This solution has a time complexity of O(n), where n is the number of nodes in the list, and a space complexity of O(1), as we only use a constant amount of extra space.
Invariant (What does not vary in this problem?)
 Do not change the order
 When you find the value remove it from the list and create the link to the element the removed element was pointing to
How to remove the element in the linked list? We cannot accomplish by using just one pointer. In Java yes, we need to make the next of 6 to be null
Two pointers approach Initialize the leader, follower to nil and first element The leader will check if the node is 6, if it is we create the link
f.next = l.next l.next = nil
f = f.next l = f.next
Terminating condition Leader.next is not null move leader and follower by one
We should return the head of the linked list If head is 6, we will have a new head
dummy = Node.new dummy.next = head
return dummy.next
Time : O(n) Space : O(1)
dummy
[1, 1]
f l
f


Identifying Problem Isomorphism
“Remove Linked List Elements” can be approximately mapped to “Move Zeroes”.
In “Remove Linked List Elements”, you’re given a linked list and a value. Your task is to remove all the nodes of the linked list that have the value equal to the given value.
Similarly, in “Move Zeroes”, you’re given an array of integers. Your task is to move all the 0’s to the end of it while maintaining the relative order of the nonzero elements.
The two problems are similar because they both involve a linear data structure (linked list or array) and require the removal or relocation of elements based on their values. However, “Move Zeroes” deals with an array and involves moving the zeros to the end, while “Remove Linked List Elements” deals with a linked list and involves removing nodes.
“Move Zeroes” is simpler because working with arrays tends to be easier than working with linked lists due to their direct access property. The similarity in the required operations makes these problems approximate isomorphs.


Problem Classification
The problem is about “Linked List Manipulation”. It can be classified as “Linked List Deletion” as the task requires removal of certain nodes from the list based on their values.
This problem falls under the category of “SinglyLinked List Operations”, as it involves understanding and manipulating the singlylinked list data structure.
This problem can be classified under “Iterative Methods” as the solution involves iterating through the linked list to achieve the desired output.
Finally, from a practical usecase perspective, this kind of problem could be classified under “Data Cleaning/Preprocessing”, as it involves removing certain data points based on their values.
Language Agnostic Coding Drills
The above code is to remove all elements from a linked list that have a specific value. Here are the concepts and steps we can break the problem into:
Understanding Linked Lists: The primary data structure used here is a linked list. Each node of the list consists of two parts: its value and a pointer to the next node. The last node points to None, indicating the end of the list.
Iteration through a Linked List: The solution needs to traverse the list. Iterating over a linked list involves starting from the head node and following the pointers until reaching a node that points to None.
Dummy Head/Node in Linked Lists: A dummy node is an artificial node that we often add at the front of the linked list to simplify edge cases where the head node might be deleted.
Node Deletion in a Linked List: To remove a node from a linked list, we change the next pointer of the node preceding it to point to the node following it. This essentially “skips over” the node to be deleted, and it’s no longer part of the list.
Conditional Checks: A conditional check is needed to determine whether or not a node’s value matches the target value to be removed.
The steps to solve this problem:
Create a dummy node and make it the new head of the linked list.
Iterate over the linked list, starting from the dummy head. For each node, check if its next node’s value is equal to the target value.
If the next node’s value equals the target value, change the current node’s next pointer to skip the next node (thus deleting it). If not, move to the next node.
Continue until you have checked all nodes in the list.
Return the next node of the dummy head, which now serves as the new head of the processed list.
Targeted Drills in Python
Drill 1: Linked List Creation and Traversal
Before we can manipulate linked lists, we first need to understand how to create and traverse through one.


Drill 2: Implementing Dummy Head
Create a dummy node and link it to the head of our linked list.


Drill 3: Linked List Node Deletion
Try to remove the second node from our linked list.


Drill 4: Conditional Checks and Node Deletion
Iterate through a linked list and remove any node that has a value of 2.


After mastering these individual drills, you should be able to understand and implement the full solution where you can pass any linked list and any value to a function, and it will return the linked list after removing all the nodes with that value.