Swap Nodes in Pairs

Given a linked list, swap every two adjacent nodes and return its head. You must solve the problem without modifying the values in the list's nodes (i.e., only nodes themselves may be changed.)

def swapPairs(head):    

    cur = head
    prev = None
    new_head = head

    while cur and cur.next:
        # Save next pair
        nn = cur.next.next
       
        # swap cur, cur.next
        a = cur
        b = cur.next
       
        if prev:
            prev.next = b
        else:
            new_head = b
           
        a.next = b.next
        b.next = a
       
         # update prev
        prev = cur
        cur = nn
       
    return new_head

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