Trapping Rain Water Problem in DSA Python - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to initialize the total trapped water to zero.

DSA Python

water = [1]

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

A0

B1

CNone

D[]

Attempts:

3 left

💡 Hint

Common Mistakes

Initializing water with 1 or None instead of 0.

We start counting trapped water from zero because initially no water is trapped.

2fill in blank

medium

Complete the code to find the maximum height to the left of the current bar.

DSA Python

left_max = max(height[:[1]])

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

Ai

Bi+1

Ci-1

Dlen(height)

Attempts:

3 left

💡 Hint

Common Mistakes

Using i+1 includes the current bar, which is incorrect.

We take all bars to the left of the current index i, so slicing up to i excludes the current bar.

3fill in blank

hard

Fix the error in the code to calculate trapped water at index i.

DSA Python

water += min(left_max, right_max) - [1]

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

Aleft_max

Bright_max

Cheight[i]

Dwater

Attempts:

3 left

💡 Hint

Common Mistakes

Subtracting left_max or right_max instead of height[i].

We subtract the height of the current bar to find how much water can be trapped above it.

4fill in blank

hard

Fill both blanks to complete the loop that iterates over the bars except the first and last.

DSA Python

for i in range([1], [2]):

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

A1

B0

Clen(height) - 1

Dlen(height)

Attempts:

3 left

💡 Hint

Common Mistakes

Starting from 0 or ending at len(height) includes bars that can't trap water.

We skip the first and last bars because they cannot trap water.

5fill in blank

hard

Fill all three blanks to complete the function that calculates trapped rain water.

DSA Python

def trap(height):
    water = [1]
    for i in range([2], [3]):
        left_max = max(height[:i])
        right_max = max(height[i+1:])
        water += min(left_max, right_max) - height[i]
    return water

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

A0

B1

Clen(height) - 1

Dlen(height)

Attempts:

3 left

💡 Hint

Common Mistakes

Incorrect loop range or water initialization.

The function initializes water to zero, loops from the second bar to the second last bar, and calculates trapped water correctly.