Stack :

• A stack is a logical concept that consists of a set of similar elements, stacks are based on the principle of last in first out (LIFO)
• for our projects we have a set of rules that we can use on our stack to work on it :
  • sa (swap a): Swap the first 2 elements at the top of stack a. Do nothing if there is only one or no elements.
  • sb (swap b): Swap the first 2 elements at the top of stack b. Do nothing if there is only one or no elements.
  • ss : sa and sb at the same time.
  • pa (push a): Take the first element at the top of b and put it at the top of a. Do nothing if b is empty.
  • pb (push b): Take the first element at the top of a and put it at the top of b. Do nothing if a is empty.
  • ra (rotate a): Shift up all elements of stack a by 1. The first element becomes the last one.
  • rb (rotate b): Shift up all elements of stack b by 1. The first element becomes the last one.
  • rr : ra and rb at the same time.
  • rra (reverse rotate a): Shift down all elements of stack a by 1. The last element becomes the first one.
  • rrb (reverse rotate b): Shift down all elements of stack b by 1. The last element becomes the first one.
  • rrr : rra and rrb at the same time