Sliding Window on Arrays in DSA Python - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to calculate the sum of the first window of size k in the array.

DSA Python

def initial_window_sum(arr, k):
    window_sum = sum(arr[[1]:k])
    return window_sum

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

A0

B-1

Ck

D1

Attempts:

3 left

💡 Hint

Common Mistakes

Starting the slice at 1 instead of 0, which misses the first element.

Using k as the start index, which results in an empty slice.

The first window starts at index 0, so we sum from index 0 to k-1.

2fill in blank

medium

Complete the code to slide the window by one position and update the sum.

DSA Python

def slide_window_sum(arr, window_sum, start, k):
    window_sum = window_sum - arr[start] + arr[start + [1]]
    return window_sum

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A1

Bk - 1

Cstart

Dk

Attempts:

3 left

💡 Hint

Common Mistakes

Using start + 1 instead of start + k, which adds the wrong element.

Using k - 1 which is off by one for the new element index.

When sliding the window, we remove the element at the start and add the element at start + k.

3fill in blank

hard

Fix the error in the code to correctly find the maximum sum of any window of size k.

DSA Python

def max_window_sum(arr, k):
    max_sum = sum(arr[0:k])
    window_sum = max_sum
    for i in range(1, len(arr) - k + 1):
        window_sum = window_sum - arr[i - 1] + arr[i + [1]]
        if window_sum > max_sum:
            max_sum = window_sum
    return max_sum

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

Ak

Bk - 1

C1

Di

Attempts:

3 left

💡 Hint

Common Mistakes

Using i + k which goes out of range.

Using i which is the start index, not the new element index.

The new element index is i + k - 1 because the window covers k elements starting at i.

4fill in blank

hard

Fill both blanks to create a dictionary of window sums keyed by the window's start index.

DSA Python

def window_sums_dict(arr, k):
    sums = {}
    current_sum = sum(arr[0:k])
    sums[0] = current_sum
    for i in range(1, len(arr) - k + 1):
        current_sum = current_sum - arr[i - [1]] + arr[i + [2]]
        sums[i] = current_sum
    return sums

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

A1

Bk

Ck - 1

D0

Attempts:

3 left

💡 Hint

Common Mistakes

Using k instead of 1 for the leaving element index.

Using k instead of k - 1 for the entering element index.

Subtract the element leaving at i-1 and add the element entering at i + k - 1.

5fill in blank

hard

Fill all three blanks to create a list of averages of each sliding window of size k.

DSA Python

def sliding_window_averages(arr, k):
    averages = []
    window_sum = sum(arr[0:k])
    averages.append(window_sum / [1])
    for i in range(1, len(arr) - k + 1):
        window_sum = window_sum - arr[i - [2]] + arr[i + [3]]
        averages.append(window_sum / k)
    return averages

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

Ak

B1

Ck - 1

D0

Attempts:

3 left

💡 Hint

Common Mistakes

Dividing by 1 instead of k for the average.

Using wrong indices for elements leaving or entering the window.

The average divides the sum by k. The element leaving is at i-1 and the entering element is at i + k - 1.