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Code Circular Linked List

Reverse a doubly circular linked list

The problem involves reversing a circular doubly linked list by swapping the values of the nodes. A circular doubly linked list is a data structure in which each node has pointers to both its previous and next nodes, and the last node's next pointer points back to the first node, creating a loop.

Problem Statement

Given a circular doubly linked list, the task is to reverse the order of its elements using a swap of node values.

Example

Consider the circular doubly linked list: 1 <-> 2 <-> 3 <-> 4 <-> 5 <-> 6. After reversing the elements, the list will become: 6 <-> 5 <-> 4 <-> 3 <-> 2 <-> 1.

Idea to Solve the Problem

To reverse the order of elements in a circular doubly linked list using a swap of node values, we need to follow these steps:

  1. Get references to the first node (front) and the last node (tail).
  2. Initialize a temporary variable (temp) to store the value during the swap operation.
  3. Traverse the list using two pointers (first and last), moving towards each other from the front and the tail respectively.
  4. Swap the values of the nodes pointed to by first and last.
  5. Continue swapping and moving the pointers until first and last meet or cross each other.
  6. The reversal is complete when first and last cross each other.

Pseudocode

Here's the pseudocode to reverse a circular doubly linked list by swapping node values:

function reverseElement():
    first = front
    last = tail
    while first is not NULL and last is not NULL:
        if first is not last:
            // Swap values of first and last nodes
            temp = first.data
            first.data = last.data
            last.data = temp
            if first.next is last:
                // Stop reversal
                first = NULL
                last = NULL
            else:
                first = first.next
                last = last.back
        else:
            // Stop reversal
            first = NULL
            last = NULL

Algorithm Explanation

  1. Get references to the first node (front) and the last node (tail).
  2. Initialize a temporary variable (temp) to store the value during the swap operation.
  3. Traverse the list using two pointers (first and last), moving towards each other from the front and the tail respectively.
  4. Swap the values of the nodes pointed to by first and last.
  5. Continue swapping and moving the pointers until first and last meet or cross each other.
  6. The reversal is complete when first and last cross each other.

Code Solution

Time Complexity

The time complexity of reversing a circular doubly linked list using a swap of node values is O(n), where n is the number of nodes in the list. This is because we iterate through the list once to perform the swap operation.

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