Delete all Even position nodes from circular linked list

In the problem of deleting all even position nodes from a circular linked list, we are working with a circular linked list data structure. The objective is to remove nodes that are at even positions (starting from index 0) from the circular linked list while maintaining its circular nature.

Problem Statement

Given a circular linked list, we need to delete all nodes that are at even positions, considering the first node as position 0. After the deletion, the circular structure of the linked list should still be preserved.

Example

Consider a circular linked list with the following elements: 12 -> 22 -> 32 -> 42 -> 52 -> 62 -> 72 -> 82. After deleting all even position nodes, the list becomes: 22 -> 42 -> 62 -> 82.

Idea to Solve the Problem

To delete all even position nodes from a circular linked list, we need to iterate through the list and remove nodes at even positions. We'll handle various cases, such as when the list is empty, contains only one node, or has more than one node.

Pseudocode

Here's the pseudocode to delete all even position nodes from a circular linked list:

function deleteEvenPositionNodes(circularLinkedList):
    if circularLinkedList.head is NULL:
        print "Empty linked list"
        return
    else if circularLinkedList.head.next is circularLinkedList.head:
        # Only one element in the list
        circularLinkedList.head = NULL
        return
    
    temp = circularLinkedList.head.next.next
    back = circularLinkedList.head.next
    
    while temp is not NULL and temp is not circularLinkedList.head:
        # Unlink deleted node
        back.next = temp.next
        temp = NULL
        # Get next even position node
        back = back.next
        if back is circularLinkedList.head:
            return
        # Visit to next deleted node
        temp = back.next
    
    # Set new head
    circularLinkedList.head = circularLinkedList.head.next
    if back is not NULL:
        # Connect last node to new head
        back.next = circularLinkedList.head

Algorithm Explanation

1. Check if the linked list is empty. If it is, print a message and return.
2. Check if the linked list has only one node. If it does, set the head to NULL and return.
3. Initialize temp and back pointers to traverse the list. back points to the previous node at an even position.
4. Traverse the list using the temp pointer, while also updating back and removing nodes at even positions.
5. After removing a node at an even position, update back to the next node, and continue the traversal.
6. If the traversal reaches the end of the list or comes back to the head, update the head and connect the last node to the new head to maintain the circular structure.

Program List

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Time Complexity

The time complexity of deleting all even position nodes from a circular linked list is O(n), where n is the number of nodes in the circular linked list. This is because we need to traverse the entire list to identify and remove even position nodes. The space complexity is O(1) as we are using only a constant amount of extra space for pointers.