Stack applications (expression evaluation, backtracking) in Data Structures Theory - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to push an element onto the stack.

Data Structures Theory

stack.[1](element)

Drag options to blanks, or click blank then click option'

Aremove

Bpop

Cpeek

Dpush

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'pop' instead of 'push' to add elements.

To add an element to the top of a stack, you use the push operation.

2fill in blank

medium

Complete the code to check if the stack is empty before popping.

Data Structures Theory

if not stack.[1]():
    stack.pop()

Drag options to blanks, or click blank then click option'

Ais_empty

Bpush

Cpeek

Dsize

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'peek' or 'size' which do not return a boolean for emptiness.

Before removing an element, you check if the stack is empty using is_empty() to avoid errors.

3fill in blank

hard

Fix the error in the expression evaluation code by completing the blank.

Data Structures Theory

while stack and precedence(stack[-1]) >= precedence([1]):
    output.append(stack.pop())

Drag options to blanks, or click blank then click option'

Acurrent_op

Bstack[-1]

Coutput[-1]

Dexpression[-1]

Attempts:

3 left

💡 Hint

Common Mistakes

Using the top of the stack instead of the current operator.

We compare the precedence of the operator on top of the stack with the current operator being processed, here named current_op.

4fill in blank

hard

Fill both blanks to correctly implement backtracking with a stack.

Data Structures Theory

stack.[1](state)
while stack:
    current = stack.[2]()

Drag options to blanks, or click blank then click option'

Apush

Bpop

Cpeek

Dremove

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'peek' or 'remove' which do not add or remove elements properly.

In backtracking, you push new states onto the stack and pop them to explore.

5fill in blank

hard

Fill all three blanks to create a dictionary comprehension that maps operators to their precedence if precedence is greater than 1.

Data Structures Theory

precedence_map = { [1]: [2] for [1], [2] in [3].items() if [2] > 1 }

Drag options to blanks, or click blank then click option'

Aop

Bprec

Coperators

Ditems

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'items' as a variable name or repeating the same variable for key and value.

This comprehension iterates over operators dictionary items, unpacking keys as op and values as prec, then filters by precedence > 1.