Evaluate Postfix Expression Using Stack in DSA Python - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to push operands onto the stack.

DSA Python

if ch.isdigit():
    stack.[1](int(ch))

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

Apush

Bremove

Cpop

Dappend

Attempts:

3 left

💡 Hint

Common Mistakes

Using pop() instead of append() to add elements.

Using push() which is not a Python list method.

In Python, list's append() method adds an element to the end of the list, which is used here to push onto the stack.

2fill in blank

medium

Complete the code to pop the top two operands from the stack.

DSA Python

op2 = stack.[1]()
op1 = stack.pop()

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

Apop

Bappend

Cremove

Dpush

Attempts:

3 left

💡 Hint

Common Mistakes

Using append() which adds elements instead of removing.

Using remove() which removes by value, not by position.

pop() removes and returns the last element from the list, which is the top of the stack.

3fill in blank

hard

Fix the error in the operation application line to correctly compute the result.

DSA Python

if ch == '+':
    res = op1 [1] op2

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

A*

B-

C+

D/

Attempts:

3 left

💡 Hint

Common Mistakes

Using '-' or '*' instead of '+'.

Using '/' which performs division.

For addition, the operator '+' must be used between operands.

4fill in blank

hard

Fill both blanks to correctly handle multiplication and division operations.

DSA Python

elif ch == '*':
    res = op1 [1] op2
elif ch == '/':
    res = op1 [2] op2

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

A*

B+

C/

D-

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up operators like using '+' for multiplication.

Using '-' for division.

Multiplication uses '*', division uses '/' operators between operands.

5fill in blank

hard

Fill all three blanks to complete the postfix evaluation function with correct stack operations and return.

DSA Python

def evaluate_postfix(expr):
    stack = []
    for ch in expr:
        if ch.isdigit():
            stack.[1](int(ch))
        else:
            op2 = stack.[2]()
            op1 = stack.pop()
            if ch == '+':
                res = op1 + op2
            elif ch == '-':
                res = op1 - op2
            elif ch == '*':
                res = op1 * op2
            elif ch == '/':
                res = op1 / op2
            stack.append(res)
    return stack.[3]()

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

Aappend

Bpop

Dremove

Attempts:

3 left

💡 Hint

Common Mistakes

Using remove() which removes by value, not position.

Mixing append and pop incorrectly.

Operands are pushed using append(), popped using pop(), and the final result is popped from the stack.