Bubble Sort Algorithm in DSA Go - Build from Scratch

Bubble Sort Algorithm

📖 Scenario: You are helping a librarian organize a small shelf of books by their ID numbers. The books are currently in a random order, and you want to arrange them from the smallest ID to the largest using a simple sorting method.

🎯 Goal: Build a program that sorts a list of book IDs using the Bubble Sort algorithm. You will create the list, set up a variable to track the number of passes, implement the sorting logic, and finally print the sorted list.

📋 What You'll Learn

Create a slice of integers called bookIDs with the exact values: 34, 12, 25, 9, 56

Create an integer variable called n that stores the length of bookIDs

Use nested for loops with variables i and j to implement the Bubble Sort algorithm

Swap adjacent elements in bookIDs if they are in the wrong order

Print the sorted bookIDs slice

💡 Why This Matters

🌍 Real World

Sorting is a common task in organizing data, like arranging books, files, or records in order.

💼 Career

Understanding sorting algorithms like Bubble Sort helps in optimizing data processing and is a foundation for learning more advanced algorithms.

1

Create the list of book IDs

Create a slice of integers called bookIDs with these exact values: 34, 12, 25, 9, 56

DSA Go

# Your code here

Hint

Use bookIDs := []int{34, 12, 25, 9, 56} to create the slice.

2

Set up the length variable

Create an integer variable called n that stores the length of the bookIDs slice

DSA Go

package main

func main() {
    bookIDs := []int{34, 12, 25, 9, 56}
    // Your code here
}

Hint

Use len(bookIDs) to get the length of the slice.

3

Implement the Bubble Sort logic

Use nested for loops with variables i and j to implement the Bubble Sort algorithm. Swap adjacent elements in bookIDs if the element at j is greater than the element at j+1

DSA Go

package main

func main() {
    bookIDs := []int{34, 12, 25, 9, 56}
    n := len(bookIDs)
    // Your code here
}

Hint

Use two for loops to compare and swap adjacent elements.

4

Print the sorted list

Print the sorted bookIDs slice using fmt.Println(bookIDs). Remember to import the fmt package at the top.

DSA Go

package main

import "fmt"

func main() {
    bookIDs := []int{34, 12, 25, 9, 56}
    n := len(bookIDs)

    for i := 0; i  bookIDs[j+1] {
                bookIDs[j], bookIDs[j+1] = bookIDs[j+1], bookIDs[j]
            }
        }
    }
    // Your code here
}

Hint

Use fmt.Println(bookIDs) to print the sorted slice.

Practice

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

easy

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

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

C. Select the smallest element and move it to the beginning

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

Solution

1. Step 1: Understand Bubble Sort mechanism

   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 sort, insertion sort.

3. Final Answer:

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

4. Quick Check:

   Bubble Sort = swapping 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
• Assuming it inserts elements like Insertion Sort

2. Which of the following is the correct way to write the outer loop for Bubble Sort in Go to sort an array arr of length n?

easy

A. for i := 0; i < n-1; i++ {}

B. for i := 0; i < n; i++ {}

C. for i := 1; i <= n; i++ {}

D. for i := 1; i < n-1; i++ {}

Solution

1. Step 1: Determine loop range for passes

   Bubble Sort requires n-1 passes to ensure sorting, so loop runs from 0 to n-2 (i < n-1).

2. Step 2: Check options for correct syntax and range

   for i := 0; i < n-1; i++ {} correctly uses i := 0; i < n-1; i++. Others either run too many or incorrect iterations.

3. Final Answer:

   for i := 0; i < n-1; i++ {} -> Option A

4. Quick Check:

   Outer loop runs n-1 times [OK]

Hint: Outer loop runs n-1 times in Bubble Sort [OK]

Common Mistakes:

• Using i <= n causing out-of-range errors
• Starting loop at 1 instead of 0
• Looping n times instead of n-1

3. What will be the output of the following Go code snippet after applying one full pass of Bubble Sort on the array?

arr := []int{5, 3, 8, 4, 2}
n := len(arr)
for j := 0; j < n-1; j++ {
    if arr[j] > arr[j+1] {
        arr[j], arr[j+1] = arr[j+1], arr[j]
    }
}
fmt.Println(arr)

medium

A. [2 3 4 5 8]

B. [3 5 8 4 2]

C. [3 5 4 2 8]

D. [5 3 8 4 2]

Solution

1. Step 1: Perform one pass of Bubble Sort

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

2. Step 2: Final array after one pass

   After one pass, largest element 8 moves to the end. Array is [3 5 4 2 8].

3. Final Answer:

   [3 5 4 2 8] -> Option C

4. Quick Check:

   One pass moves largest to end [OK]

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

Common Mistakes:

• Assuming full sort after one pass
• Not swapping correctly
• Confusing indices in swaps

4. Identify the error in the following Bubble Sort code snippet in Go:

arr := []int{4, 2, 7, 1}
n := len(arr)
for i := 0; i < n; i++ {
    for j := 0; j < n; j++ {
        if arr[j] > arr[j+1] {
            arr[j], arr[j+1] = arr[j+1], arr[j]
        }
    }
}
fmt.Println(arr)

medium

A. Outer loop should start from 1 instead of 0

B. Inner loop runs out of range causing runtime error

C. Swap condition should be arr[j] < arr[j+1]

D. Array length n is incorrect

Solution

1. Step 1: Analyze inner loop range

   Inner loop runs j from 0 to n-1, but accesses arr[j+1]. When j = n-1, arr[j+1] is out of range causing runtime error.

2. Step 2: Correct inner loop range

   Inner loop should run from 0 to n-2 (j < n-1) to avoid out-of-range access.

3. Final Answer:

   Inner loop runs out of range causing runtime error -> Option B

4. Quick Check:

   Index out of range error = inner loop limit [OK]

Hint: Inner loop must stop before last index to avoid out-of-range [OK]

Common Mistakes:

• Not adjusting inner loop limit
• Swapping with wrong comparison
• Misunderstanding loop boundaries

5. Given the array arr := []int{3, 1, 4, 5, 2}, how many total swaps will Bubble Sort perform to fully sort the array in ascending order?

hard

A. 5

B. 7

C. 6

D. 4

Solution

1. Step 1: Trace swaps in each pass

   Initial array: [3,1,4,5,2] Pass 1: - 3 > 1 swap -> [1,3,4,5,2] (1 swap) - 3 > 4 no swap - 4 > 5 no swap - 5 > 2 swap -> [1,3,4,2,5] (2 swaps total) Pass 2: - 1 > 3 no swap - 3 > 4 no swap - 4 > 2 swap -> [1,3,2,4,5] (3 swaps total) Pass 3: - 1 > 3 no swap - 3 > 2 swap -> [1,2,3,4,5] (4 swaps total) Pass 4: - 1 > 2 no swap - 2 > 3 no swap No swaps, sorting done.

2. Step 2: Count total swaps

   Pass 1: 2 swaps Pass 2: 1 swap Pass 3: 1 swap Total = 4 swaps Recheck carefully: Pass 1: swaps at (3,1) and (5,2) = 2 Pass 2: swap at (4,2) = 1 Pass 3: swap at (3,2) = 1 Total swaps = 4

3. Step 3: Verify if more swaps needed

   Sorting completes after pass 4 with no swaps. Total swaps = 4

4. Final Answer:

   4 -> Option D

5. Quick Check:

   Count swaps carefully per pass [OK]

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

Common Mistakes:

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