Pedagogical issues with Stack Implementation

manpreet Best Answer 3 years ago

I am new to teaching the particular syllabus I have been asked to teach and I am confused by the approach given for several of the algorithms. For example the stack implementation based on the course materials given below seems very convoluted. I'm curious to hear if others would share my concerns if they had to teach about stacks in this way, or if they can offer any insight into the advantages of this approach.

The concerns I have which I'm curious to hear your opinion about are:

• Using the call by reference approach makes the push and pop calls very unwieldy

• It looks like new items are added to the end of the list, making the algorithm O(n) rather than O(1)

• The algorithm is hard to follow (IMO)

• It is possible to implement a stack in a much simpler fashion, which would allow student to focus more on conceptual understanding of the behavior and use of stacks, and to see the link between the concept and the implementation more clearly.

# NullPointer should be set to -1 if using array element with index 0
NULLPOINTER = -1

#Declare record type to store data and pointer
class Node:
        def __init__(self):
                self.Data = ""
                self.Pointer = NULLPOINTER

def InitialiseStack():
        Stack = [Node() for i in range(8)]
        TopOfStack = NULLPOINTER  # set start pointer
        FreeListPtr = 0  # set starting position of free ist
        for Index in range(7):
                Stack[Index].Pointer = Index + 1
        Stack[7].Pointer = NULLPOINTER  # last node of free list
        return (Stack, TopOfStack, FreeListPtr)


def Push(Stack, TopOfStack, FreeListPtr, NewItem):
        if FreeListPtr != NULLPOINTER:
        # there is space in the array
        # take node from free list and store data item
                NewNodePtr = FreeListPtr
                Stack[NewNodePtr].Data = NewItem
                FreeListPtr = Stack[FreeListPtr].Pointer
                # insert new node at top of stack
                Stack[NewNodePtr].Pointer = TopOfStack
                TopOfStack = NewNodePtr
        else:
                print("no space for more data")
        return (Stack, TopOfStack, FreeListPtr)


def Pop(Stack, TopOfStack, FreeListPtr):
        if TopOfStack == NULLPOINTER:
                print("no data on stack")
                Value = ""
        else:
                Value = Stack[TopOfStack].Data
                ThisNodePtr = TopOfStack
                TopOfStack = Stack[TopOfStack].Pointer
                Stack[ThisNodePtr].Pointer = FreeListPtr
                FreeListPtr = ThisNodePtr
                return (Stack, TopOfStack, FreeListPtr, Value)

def OutputAllNodes(Stack, TopOfStack) :
        CurrentNodePtr = TopOfStack # start at beginning of list
        if TopOfStack ==
                                                

                                                                                                        
                                                    
                                                
                                                

                                                    

                                                        
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