Trapping Rain Water Using Stack in DSA Python - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to initialize an empty stack for storing indices.

DSA Python

stack = [1]

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

A[]

B{}

C()

Dset()

Attempts:

3 left

💡 Hint

Common Mistakes

Using curly braces {} creates a dictionary, not a stack.

Using parentheses () creates a tuple, which is immutable.

We use a list [] as a stack to store indices of bars.

2fill in blank

medium

Complete the code to pop the top element from the stack.

DSA Python

top = stack.[1]()

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

Apop

Bremove

Cdelete

Ddiscard

Attempts:

3 left

💡 Hint

Common Mistakes

Using remove() causes errors because it expects a value, not an index.

Using delete is not a list method.

The pop() method removes and returns the last item from the list, acting as stack pop.

3fill in blank

hard

Fix the error in the condition to check if the stack is not empty.

DSA Python

while stack and height[i] > height[[1]]:

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

Astack.pop()

Bstack[0]

Cstack

Dstack[-1]

Attempts:

3 left

💡 Hint

Common Mistakes

Using stack[0] compares with the bottom element, causing wrong logic.

Using stack.pop() removes the element, which is incorrect here.

We compare with the height at the index on top of the stack, which is stack[-1].

4fill in blank

hard

Fill both blanks to calculate the distance and bounded height for trapped water.

DSA Python

distance = i - [1] - 1
bounded_height = min(height[i], height[[2]]) - height[top]

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

Astack[-1]

Btop

Cstack[0]

Di

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong indices for distance causes incorrect water calculation.

Mixing up top and stack[-1] leads to errors.

Distance is between current index i and the new top of stack stack[-1]. Bounded height is min(height[stack[-1]], height[i]) - height[top].

5fill in blank

hard

Fill all three blanks to update the total trapped water and push current index to stack.

DSA Python

water += distance * bounded_height
stack.[1](i)
i += [2]

# Loop condition
while i < [3]:

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

Aappend

B1

Clen(height)

Dpop

Attempts:

3 left

💡 Hint

Common Mistakes

Using pop instead of append removes elements incorrectly.

Incrementing i by wrong value causes infinite loops.

Looping beyond length causes index errors.

We add trapped water, push current index with append, increment i by 1, and loop while i is less than the length of the height list.