def top(self): #returns the top element
#complexity O(1)
x = Option()
if self.__elements.emptyList():
x.setOp(False)
else:
x.setEl(self.__elements.getEl(0))
return x #returns empty option if list is empty
def dequeue(self): #deletes the last elemet in the fill
#complexity O(n) if empty is empty else complexity O(1)
if self.__empty.emptyList():
if self.__fill.emptyList():
raise Exception("Queue is Empty")
self.__empty = self.__fill.reverse(Nil()) #takes linear time
self.__fill = Nil()
op = Option()
if self.isEmpty():
op.setOp(False)
else:
op.setEl(self.__empty.getEl(0))
self.__empty.deletFirst()
return op #returns the value
