Subarray Sum Equals K Using Hash Map in DSA Python - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to initialize the count of subarrays to zero.

DSA Python

count = [1]

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

ANone

B1

C-1

D0

Attempts:

3 left

💡 Hint

Common Mistakes

Starting count from 1 or None instead of 0.

We start counting subarrays from zero because initially we have found none.

2fill in blank

medium

Complete the code to update the cumulative sum with the current number.

DSA Python

cumulative_sum [1] num

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A+=

B/=

C*=

D-=

Attempts:

3 left

💡 Hint

Common Mistakes

Using subtraction or multiplication instead of addition.

We add the current number to the cumulative sum to keep track of the total so far.

3fill in blank

hard

Fix the error in checking if (cumulative_sum - k) exists in the hash map.

DSA Python

if (cumulative_sum [1] k) in prefix_sums:

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A+

B-

C*

D/

Attempts:

3 left

💡 Hint

Common Mistakes

Using addition or multiplication instead of subtraction.

We subtract k from cumulative_sum to find if a previous prefix sum exists that forms a subarray summing to k.

4fill in blank

hard

Fill both blanks to update the hash map with the current cumulative sum count.

DSA Python

prefix_sums[cumulative_sum] = prefix_sums.get([1], 0) [2] 1

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Acumulative_sum

B+

C-

Dcount

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong key or subtracting instead of adding.

We get the current count of cumulative_sum in the map and add 1 to update it.

5fill in blank

hard

Fill all three blanks to complete the function that returns the count of subarrays summing to k.

DSA Python

def subarray_sum(nums, k):
    count = 0
    cumulative_sum = 0
    prefix_sums = [1]
    prefix_sums[0] = 1
    for num in nums:
        cumulative_sum [2] num
        if (cumulative_sum - k) in prefix_sums:
            count += prefix_sums[cumulative_sum - k]
        prefix_sums[cumulative_sum] = prefix_sums.get(cumulative_sum, 0) [3] 1
    return count

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

A{}

B+=

Cdefaultdict(int)

D+

Attempts:

3 left

💡 Hint

Common Mistakes

Using defaultdict without import, wrong operators, or wrong dictionary initialization.

We use a normal dictionary to store prefix sums, add current number to cumulative_sum, and add 1 to the count in the dictionary.