Bubble Sort Algorithm in DSA Python - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to swap two elements in the list.

DSA Python

if arr[j] > arr[j[1]1]:
    arr[j], arr[j+1] = arr[j+1], arr[j]

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

A+

B-

C*

D/

Attempts:

3 left

💡 Hint

Common Mistakes

Using '-' instead of '+' causes index errors.

Using '*' or '/' does not make sense for indexing.

We use j + 1 to compare the current element with the next one.

2fill in blank

medium

Complete the code to run the inner loop for bubble sort.

DSA Python

for j in range(0, n[1]i[2]1):
    if arr[j] > arr[j+1]:
        arr[j], arr[j+1] = arr[j+1], arr[j]

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

A-

B+

C*

D/

Attempts:

3 left

💡 Hint

Common Mistakes

Using '+' causes index out of range errors.

Using '*' or '/' is incorrect for loop ranges.

The inner loop runs until n - i - 1 to avoid checking sorted elements.

3fill in blank

hard

Fix the error in the outer loop range for bubble sort.

DSA Python

for i in range([1]):
    for j in range(0, n - i - 1):
        if arr[j] > arr[j+1]:
            arr[j], arr[j+1] = arr[j+1], arr[j]

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

An

Bn+1

Cn-1

Di

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'n+1' causes an extra unnecessary pass.

Using 'n-1' misses sorting the last element.

Using 'i' is incorrect as it is the loop variable.

The outer loop runs from 0 to n to cover all elements.

4fill in blank

hard

Fill both blanks to complete the bubble sort function header and return statement.

DSA Python

def bubble_sort([1]):
    n = len(arr)
    for i in range(n):
        for j in range(0, n - i - 1):
            if arr[j] > arr[j+1]:
                arr[j], arr[j+1] = arr[j+1], arr[j]
    return [2]

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

Aarr

Blist

Carray

Ddata

Attempts:

3 left

💡 Hint

Common Mistakes

Using different names for parameter and return causes errors.

Using generic names like 'list' or 'data' without matching the code.

The function takes arr as input and returns the sorted arr.

5fill in blank

hard

Fill all three blanks to create a dictionary comprehension that maps indices to elements greater than 5.

DSA Python

count_greater = [1]: [2] for [3], [2] in enumerate(arr) if [2] > 5}

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

A{i

Bx

Di

Attempts:

3 left

💡 Hint

Common Mistakes

Using inconsistent variable names.

Missing the condition to filter elements greater than 5.

This comprehension creates a dictionary with keys as indices and values as elements greater than 5.

Practice

1. What is the main idea behind the Bubble Sort algorithm?

easy

A. Divide the list into halves and sort each half separately

B. Repeatedly swap adjacent elements if they are in the wrong order

C. Select the smallest element and place it at the beginning

D. Use a pivot to partition the list into smaller parts

Solution

1. Step 1: Understand Bubble Sort process

   Bubble Sort compares adjacent elements and swaps them if they are out of order.

2. Step 2: Compare with other sorting methods

   Other options describe different algorithms: divide and conquer, selection, and quicksort.

3. Final Answer:

   Repeatedly swap adjacent elements if they are in the wrong order -> Option B

4. Quick Check:

   Bubble Sort = Swap adjacent pairs [OK]

Hint: Bubble Sort swaps neighbors repeatedly until sorted [OK]

Common Mistakes:

• Confusing Bubble Sort with Selection Sort
• Thinking it divides the list like Merge Sort
• Mixing it up with Quick Sort pivot method

2. Which of the following is the correct syntax to start a bubble sort outer loop in Python for a list arr of length n?

easy

A. for i in range(n):

B. for i in range(1, n):

C. for i in range(n-1):

D. for i in range(n+1):

Solution

1. Step 1: Understand loop range for bubble sort

   The outer loop runs from 0 to n-2 because we compare pairs up to the second last element.

2. Step 2: Check each option's range

   for i in range(n-1): uses range(n-1), which means 0 to n-2, correct for bubble sort outer loop.

3. Final Answer:

   for i in range(n-1): -> Option C

4. Quick Check:

   Outer loop runs n-1 times [OK]

Hint: Outer loop runs n-1 times for bubble sort [OK]

Common Mistakes:

• Using range(n) causes extra unnecessary iteration
• Starting loop at 1 misses first element
• Using range(n+1) causes index errors

3. What will be the output of the following code?

arr = [4, 2, 3]
for i in range(len(arr)-1):
    for j in range(len(arr)-1-i):
        if arr[j] > arr[j+1]:
            arr[j], arr[j+1] = arr[j+1], arr[j]
print(arr)

medium

A. [2, 3, 4]

B. [4, 3, 2]

C. [3, 2, 4]

D. [2, 4, 3]

Solution

1. Step 1: Trace first outer loop iteration (i=0)

   Inner loop runs j=0 to 1. Swaps 4 and 2 -> [2,4,3], then swaps 4 and 3 -> [2,3,4].

2. Step 2: Trace second outer loop iteration (i=1)

   Inner loop runs j=0 only. Compares 2 and 3, no swap needed. Array stays [2,3,4].

3. Final Answer:

   [2, 3, 4] -> Option A

4. Quick Check:

   Bubble Sort sorts ascending -> [2,3,4] [OK]

Hint: Bubble Sort outputs sorted list ascending [OK]

Common Mistakes:

• Not swapping correctly in inner loop
• Confusing loop ranges causing partial sort
• Printing before sorting completes

4. Identify the error in this bubble sort code snippet:

def bubble_sort(arr):
    n = len(arr)
    for i in range(n-1):
        for j in range(n-1):
            if arr[j] > arr[j+1]:
                arr[j], arr[j+1] = arr[j+1], arr[j]
    return arr

medium

A. Inner loop should run till n-1-i, not n-1

B. Outer loop should run till n-1, not n

C. Swap syntax is incorrect

D. Function does not return anything

Solution

1. Step 1: Analyze inner loop range

   Inner loop runs from 0 to n-2 always, not reducing with i, causing unnecessary comparisons.

2. Step 2: Correct inner loop range

   It should be range(n-1-i) to avoid checking already sorted elements at the end.

3. Final Answer:

   Inner loop should run till n-1-i, not n-1 -> Option A

4. Quick Check:

   Inner loop shrinks each pass [OK]

Hint: Inner loop shrinks by i each outer iteration [OK]

Common Mistakes:

• Not reducing inner loop range wastes time
• Incorrect swap syntax causes errors
• Forgetting to return sorted array

5. Given the list arr = [5, 1, 4, 2, 8], how many total swaps will bubble sort perform to sort it in ascending order?

hard

A. 4

B. 7

C. 6

D. 5

Solution

1. Step 1: Trace Pass 1 (i=0)

   Initial: [5,1,4,2,8]
   j=0: 5>1 swap [1,5,4,2,8] (1)
   j=1: 5>4 swap [1,4,5,2,8] (2)
   j=2: 5>2 swap [1,4,2,5,8] (3)
   j=3: 5<8 no swap.

2. Step 2: Trace Pass 2 (i=1)

   j=0: 1<4 no
   j=1: 4>2 swap [1,2,4,5,8] (4)
   j=2: 4<5 no.

3. Step 3: Trace Pass 3 (i=2)

   j=0: 1<2 no
   j=1: 2>4 no swap (no swap)
   No swaps in this pass.

4. Step 4: Trace Pass 4 (i=3)

   j=0: 1<2 no swap
   No swaps in this pass.

5. Step 5: Total swaps

   Total swaps so far: 4 (Pass 1) + 1 (Pass 2) = 5 swaps. But we missed one swap in Pass 2 or 3? Let's re-check.

6. Re-check Pass 2

   j=1: 4>2 swap (4th swap)
   j=2: 4<5 no swap

7. Pass 3

   j=0: 1<2 no swap
   j=1: 2<4 no swap

8. Pass 4

   j=0: 1<2 no swap

9. Step 6: Final count

   Total swaps = 4 (Pass 1) + 1 (Pass 2) = 5 swaps.

10. Final Answer:

    5 -> Option D

11. Quick Check:

    Count swaps carefully by tracing each pass [OK]

Hint: Count swaps by tracing each adjacent pair swap [OK]

Common Mistakes:

• Counting comparisons instead of swaps
• Missing swaps in later passes
• Assuming swaps equal number of elements