Linked List in Zig-Zag fashion (Greater Smaller Zig-Zag)

PROBLEM :

Given a Linked list, rearrange it such that converted list should be of the form a < b > c < d > e < f .. where a, b, c are consecutive data node of linked list and such that the order of linked list is sustained.
For example: In 11 15 20 5 10 we consider only 11 20 5 15 10 because it satisfies the above condition and the order of linked list. 5 20 11 15 10 is not considered as it does not follow the order of linked list.

Input:
You have to complete the method which takes 1 argument: the head of the  linked list. You should not read any input from stdin/console. There are multiple test cases. For each test case, this method will be called individually.

Output:
Your function should return a pointer to the zig zack linked list.

Constraints:
1 <=T<= 100
1 <= size of linked list(a) <= 1000

Example:
Input:
2
4
1 2 3 4
5
11 15 20 5 10

Output:
1 3 2 4
11 20 5 15 10

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SIMPLE c++ IMPLEMENTATION :
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/*

The structure of linked list is the following

struct Node
{
int data;
Node* next;
};

*/

void swap(Node *,Node *) ;

Node *zigZack(Node* head)
{
    if(head==NULL)
        return head ;
       
    Node *curr ;
    bool temp ;
   
    curr=head ;
    temp=true ;
   
    while(curr->next!=NULL)
    {
        if(temp)
        {
            if(curr->data>curr->next->data)
                swap(curr,curr->next) ;
        }
        else
        {
            if(curr->data<curr->next->data)
                swap(curr,curr->next) ;
        }
        curr=curr->next ;
        temp=!temp ;
    }
    return head ;
}

void swap(Node *first,Node *second)
{
    int temp ;
    temp=first->data ;
    first->data=second->data ;
    second->data=temp ;
}

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