Reverse the linked list in pairs.

The question is like this – if you have a linked list that holds 1 -> 2 -> 3 -> 4 -> X, then after the function has been called the linked list would hold 2 -> 1 -> 4 -> 3 -> X.

Solution :

public void reversePairRecursive(Node n)
{
int temp;
if(n==null || n.next ==null)
return; //base case for empty or 1 element list
else
{
//Reverse first pair
temp = n.data;
n.data = n.next.data;
n.next.data = temp;

//Call the method recursively for the rest of the list
reversePairRecursive(n.next.next);
}

}
/**
* Reverse the linkedlist in pairs -Iterative version
* @param n
*/
public void reversePairIterative()
{
Node current = head;
int temp;

while(current != null && current.next != null)
{
//Swap the pair
temp = current.data;
current.data = current.next.data;
current.next.data= temp;

//Advance the current pointer twice
current = current.next.next;
}
}