Bubble Sort Algorithm in DSA Java - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to swap two elements in the array.

DSA Java

int temp = arr[j];
arr[j] = arr[[1]];
arr[[1]] = temp;

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

Ai + 1

B0

Ci - 1

Dj + 1

Attempts:

3 left

💡 Hint

Common Mistakes

Using the wrong index for swapping causes incorrect sorting.

Swapping with a fixed index like 0 instead of the next element.

In bubble sort, we swap the current element arr[j] with the next element arr[j + 1] when they are out of order.

2fill in blank

medium

Complete the code to compare two adjacent elements in the array.

DSA Java

if (arr[j] > arr[[1]]) {
    // swap elements
}

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

Aj + 1

B0

Cj

Di

Attempts:

3 left

💡 Hint

Common Mistakes

Comparing the wrong elements leads to incorrect sorting.

Using the same index for both elements.

We compare the current element arr[j] with the next element arr[j + 1] to decide if a swap is needed.

3fill in blank

hard

Fix the error in the loop condition to avoid out-of-bound errors.

DSA Java

for (int j = 0; j < arr.length [1] 1; j++) {
    // inner loop body
}

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 bounds error.

Using '*' or '/' is not valid for loop conditions.

The inner loop should run until arr.length - 1 to avoid accessing beyond the array size.

4fill in blank

hard

Fill both blanks to complete the nested loops for bubble sort.

DSA Java

for (int [1] = 0; [1] < arr.length - 1; [1]++) {
    for (int [2] = 0; [2] < arr.length - 1 - [1]; [2]++) {
        // compare and swap
    }
}

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

Ai

Bj

Ck

Dn

Attempts:

3 left

💡 Hint

Common Mistakes

Using the same variable name for both loops.

Using variables that don't match the swap logic.

The outer loop uses i to track passes, and the inner loop uses j to compare adjacent elements.

5fill in blank

hard

Fill all three blanks to complete the swap and comparison in bubble sort.

DSA Java

if (arr[[1]] > arr[[2]]) {
    int temp = arr[[3]];
    arr[[1]] = arr[[2]];
    arr[[2]] = temp;
}

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

Aj

Bj + 1

Ci

Di + 1

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up indices causes wrong elements to swap.

Using i instead of j in the inner loop.

We compare arr[j] and arr[j + 1], then swap these two elements if needed.

Practice

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

easy

A. Insert each element into its correct position in a sorted sublist

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

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

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

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: insertion sort (A), divide and conquer (B), quicksort (C).

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 quicksort or merge sort
• Thinking bubble sort divides the list
• Assuming bubble sort inserts elements directly

2. Which of the following is the correct syntax to swap two elements arr[i] and arr[i+1] in Java during bubble sort?

easy

A. int temp = arr[i]; arr[i] = arr[i+1]; arr[i+1] = temp;

B. arr[i] = arr[i+1]; arr[i+1] = arr[i];

C. swap(arr[i], arr[i+1]);

D. int temp = arr[i+1]; arr[i] = arr[i+1]; arr[i+1] = temp;

Solution

1. Step 1: Understand swapping in Java arrays

   To swap, use a temporary variable to hold one value, then assign values accordingly.

2. Step 2: Check each option

   int temp = arr[i]; arr[i] = arr[i+1]; arr[i+1] = temp; correctly uses a temp variable. arr[i] = arr[i+1]; arr[i+1] = arr[i]; overwrites arr[i] before saving it. swap(arr[i], arr[i+1]); is invalid syntax in Java. int temp = arr[i+1]; arr[i] = arr[i+1]; arr[i+1] = temp; overwrites arr[i] without saving original arr[i].

3. Final Answer:

   int temp = arr[i]; arr[i] = arr[i+1]; arr[i+1] = temp; -> Option A

4. Quick Check:

   Use temp variable to swap [OK]

Hint: Always use a temp variable to swap two array elements [OK]

Common Mistakes:

• Overwriting one element before saving it
• Using a swap function that doesn't exist in Java
• Swapping without a temporary variable

3. What will be the output array after one full pass of bubble sort on int[] arr = {5, 3, 8, 4, 2}?

medium

A. [3, 5, 8, 4, 2]

B. [2, 3, 4, 5, 8]

C. [5, 3, 4, 2, 8]

D. [3, 5, 4, 2, 8]

Solution

1. Step 1: Perform one pass of bubble sort

   Compare and swap adjacent elements if needed:
   5 and 3: swap -> [3,5,8,4,2]
   5 and 8: no swap
   8 and 4: swap -> [3,5,4,8,2]
   8 and 2: swap -> [3,5,4,2,8]

2. Step 2: Result after first pass

   The largest element 8 moves to the end. The array is [3,5,4,2,8].

3. Final Answer:

   [3, 5, 4, 2, 8] -> Option D

4. Quick Check:

   One pass moves largest to end [OK]

Hint: One pass pushes largest element to the end [OK]

Common Mistakes:

• Not swapping all needed pairs in one pass
• Assuming full sort after one pass
• Confusing order of swaps

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

for (int i = 0; i < arr.length; i++) {
  for (int j = 0; j < arr.length; j++) {
    if (arr[j] > arr[j+1]) {
      int temp = arr[j];
      arr[j] = arr[j+1];
      arr[j+1] = temp;
    }
  }
}

medium

A. Inner loop should run till arr.length - i - 1 to avoid index out of bounds

B. Outer loop should start from 1 instead of 0

C. Swap logic is incorrect, should swap arr[j+1] with arr[j-1]

D. No error, code is correct

Solution

1. Step 1: Analyze inner loop range

   Inner loop runs till arr.length, but accesses arr[j+1]. When j = arr.length - 1, arr[j+1] causes index out of bounds.

2. Step 2: Correct inner loop limit

   Inner loop should run till arr.length - i - 1 to avoid out of bounds and optimize sorting.

3. Final Answer:

   Inner loop should run till arr.length - i - 1 to avoid index out of bounds -> Option A

4. Quick Check:

   Prevent arr[j+1] out of bounds by limiting inner loop [OK]

Hint: Inner loop limit must prevent arr[j+1] overflow [OK]

Common Mistakes:

• Ignoring array index limits in inner loop
• Incorrect swap indices
• Assuming code runs without error

5. Given an array int[] arr = {4, 2, 7, 1, 3}, how many total swaps will bubble sort perform to fully sort the array?

hard

A. 7

B. 5

C. 6

D. 8

Solution

1. Step 1: Count swaps in each pass

   Pass 1:
   4>2 swap (1)
   4>7 no swap
   7>1 swap (2)
   7>3 swap (3)
   Array: [2,4,1,3,7]
   Pass 2:
   4>1 swap (4)
   4>3 swap (5)
   Array: [2,1,3,4,7]
   Pass 3:
   2>1 swap (6)
   Array: [1,2,3,4,7]
   Pass 4:
   No swaps

2. Step 2: Total swaps

   Total swaps = 6 swaps counted in passes 1-3.

3. Final Answer:

   6 -> Option C

4. Quick Check:

   Count swaps carefully per pass [OK]

Hint: Count swaps each pass until no swaps occur [OK]

Common Mistakes:

• Counting comparisons instead of swaps
• Missing swaps in later passes
• Assuming swaps equal to array length