Prefix Sum Array in DSA Python - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to initialize the prefix sum array with the first element of the input array.

DSA Python

prefix_sum = [[1]]

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

Aarr[0]

B0

C[]

Darr

Attempts:

3 left

💡 Hint

Common Mistakes

Initializing prefix_sum as an empty list instead of starting with the first element.

Using 0 instead of the first element of the array.

The prefix sum array starts with the first element of the input array.

2fill in blank

medium

Complete the code to append the sum of the last prefix sum and the current element to the prefix sum array.

DSA Python

for i in range(1, len(arr)):
    prefix_sum.append(prefix_sum[-1] [1] arr[i])

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

A/

B-

C*

D+

Attempts:

3 left

💡 Hint

Common Mistakes

Using subtraction or multiplication instead of addition.

Using the wrong operator causing incorrect prefix sums.

Each prefix sum is the sum of the previous prefix sum and the current element.

3fill in blank

hard

Fix the error in the code to correctly compute the prefix sum array.

DSA Python

prefix_sum = [arr[0]]
for i in range(1, len(arr)):
    prefix_sum.append(prefix_sum[i-1] [1] arr[i])

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

A*

B-

C+

D//

Attempts:

3 left

💡 Hint

Common Mistakes

Using subtraction or multiplication instead of addition.

Using integer division which changes the sum.

The prefix sum at index i is the sum of prefix_sum at i-1 and arr at i.

4fill in blank

hard

Fill both blanks to create a dictionary comprehension that maps each element to its prefix sum if the element is greater than 0.

DSA Python

{word: [1] for word in arr if word [2] 0}

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Aprefix_sum[arr.index(word)]

Bprefix_sum[word]

C>

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Using the word itself as index causing errors.

Using wrong comparison operators.

The dictionary maps each word to its prefix sum using the index, and filters words greater than 0.

5fill in blank

hard

Fill all three blanks to create a dictionary comprehension that maps the uppercase of each key to its prefix sum value if the value is positive.

DSA Python

result = [1]: [2] for k, v in data.items() if v [3] 0}

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

Ak.upper()

Bv

C>

Dk.lower()

Attempts:

3 left

💡 Hint

Common Mistakes

Using lowercase keys instead of uppercase.

Including values that are zero or negative.

The dictionary comprehension maps uppercase keys to their values only if the value is greater than zero.