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Given a linked list, reverse alternate nodes and append at the end?

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Given a linked list, reverse alternate nodes and append at the end?
posted Apr 16, 2014 by Atul Mishra

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1 Answer

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Suppose Your Input is 2->4->6->8->0 The expected output is 2->6->0->8->4

The idea is to maintain two linked lists, one list of all odd positioned nodes (2, 6, 0 in above example) and other list of all even positioned nodes (6 and 8 in above example).

Algorithm
1) Traverse the given linked list which is considered as odd list. Do following for every visited node.
……a) If the node is even node, remove it from odd list and add it to the front of even node list. Nodes are added at front to keep the reverse order.
2) Append the even node list at the end of odd node list.

void rearrange(struct node *odd)
{
    // If linked list has less than 3 nodes, no change is required
    if (odd == NULL || odd->next == NULL || odd->next->next == NULL)
        return;

    // even points to the beginning of even list
    struct node *even = odd->next;

    // Remove the first even node
    odd->next = odd->next->next;

    // odd points to next node in odd list
    odd = odd->next;

    // Set terminator for even list
    even->next = NULL;

    // Traverse the  list
    while (odd && odd->next)
    {
       // Store the next node in odd list 
       struct node *temp = odd->next->next;

       // Link the next even node at the beginning of even list
       odd->next->next = even;
       even = odd->next;

       // Remove the even node from middle
       odd->next = temp;

       // Move odd to the next odd node
       if (temp != NULL)
         odd = temp;
    }

    // Append the even list at the end of odd list
    odd->next = even;
}
answer Apr 17, 2014 by Chahat Sharma
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