Count Inversions in Array in DSA Python - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to count inversions by comparing pairs.

DSA Python

def count_inversions(arr):
    count = 0
    for i in range(len(arr)):
        for j in range(i + 1, len(arr)):
            if arr[i] [1] arr[j]:
                count += 1
    return count

print(count_inversions([2, 4, 1, 3, 5]))

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

A>

B<

C==

D<=

Attempts:

3 left

💡 Hint

Common Mistakes

Using '<' instead of '>' causes counting non-inversions.

Using '==' counts equal pairs, which is incorrect.

We count an inversion when a number is greater than a number that comes after it.

2fill in blank

medium

Complete the code to merge two sorted halves and count split inversions.

DSA Python

def merge_count(left, right):
    i = j = 0
    merged = []
    count = 0
    while i < len(left) and j < len(right):
        if left[i] [1] right[j]:
            merged.append(left[i])
            i += 1
        else:
            merged.append(right[j])
            count += len(left) - i
            j += 1
    merged += left[i:]
    merged += right[j:]
    return merged, count

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

A>

B<

C<=

D>=

Attempts:

3 left

💡 Hint

Common Mistakes

Using '>' causes wrong merge order.

Using '>=' or '<=' can cause incorrect counting.

We pick from left if left[i] is less than right[j] to keep order.

3fill in blank

hard

Fix the error in the recursive function to count inversions using merge sort.

DSA Python

def sort_count(arr):
    if len(arr) <= 1:
        return arr, 0
    mid = len(arr) // 2
    left, left_count = sort_count(arr[:mid])
    right, right_count = sort_count(arr[mid:])
    merged, split_count = merge_count(left, right)
    return merged, left_count [1] right_count + split_count

print(sort_count([2, 3, 8, 6, 1])[1])

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A+

B*

C-

D/

Attempts:

3 left

💡 Hint

Common Mistakes

Using '-' subtracts counts incorrectly.

Using '*' or '/' causes wrong results.

We add counts from left, right, and split inversions to get total.

4fill in blank

hard

Complete the code to create a dictionary of word lengths for words longer than 3 letters.

DSA Python

words = ['apple', 'bat', 'carrot', 'dog', 'elephant']
lengths = {word: len(word) for word in words if len(word) [1] 3}
print(lengths)

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A:

B>

C<

D=

Attempts:

3 left

💡 Hint

Common Mistakes

Using '=' instead of ':' in dictionary comprehension.

Using '<' instead of '>' in filter condition.

Use ':' to map word to length, and '>' to filter words longer than 3.

5fill in blank

hard

Fill all three blanks to create a filtered dictionary with uppercase keys and values greater than 0.

DSA Python

data = {'a': 1, 'b': -2, 'c': 3}
result = [1]: [2] for k, v in data.items() if v [3] 0}}
print(result)

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

Ak.upper()

Bv

C>

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Using '<' instead of '>' filters wrong values.

Using k instead of k.upper() keeps keys lowercase.

Keys are uppercase k, values are v, and filter keeps values > 0.