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Pairwise swap elements of a given linked list by changing links

Pairwise swap elements of a given linked list by changing links - 

 class Solution(object): 

         #Iterative Solution 
        def swapPairs(self, head): 
        """ 
        :type head: ListNode 
        :rtype: ListNode 
        """ 
        if(head is None or head.next is None): 
            return head 
             
        curr = head.next 
        prev = head 
        head = curr 
         
        while(True): 
            sec = curr.next 
            curr.next = prev 
             
            if(sec is None or sec.next is None): 
                prev.next = sec 
                break 
             
            prev.next = sec.next 
            prev = sec 
            curr.next = prev 
        return head 
      
     #Recursively Solution
    def swapPairs(self, head): 
        """ 
        :type head: ListNode 
        :rtype: ListNode 
        """ 
        if not head or not head.next: 
            return head 
        sec = head.next 
        head.next = self.swapPairs(sec.next) 
        sec.next = head 
        return sec 
   
Reference - http://www.geeksforgeeks.org/pairwise-swap-elements-of-a-given-linked-list-by-changing-links/

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