Implement the Stack family instance method flip declared as follows (this is a Stack):

/**

* Reverses ("flips") {@code this}.

*

* @updates this

* @ensures this = rev(#this)

*/

public void flip();

Implement the Sequence family instance method flip declared as follows (this is a Sequence):

/**

* Reverses ("flips") {@code this}.

*

* @updates this

* @ensures this = rev(#this)

*/

public void flip();

Provide a second, different implementation of the instance method flip for Sequence. If your first implementation is iterative (i.e., uses a loop), your second one should be recursive and vice versa.