Bubble Sort Algorithm in DSA Javascript - Build from Scratch

Bubble Sort Algorithm

📖 Scenario: You have a list of numbers that you want to arrange from smallest to largest, like sorting books by height on a shelf.

🎯 Goal: Build a program that sorts a list of numbers using the Bubble Sort method, which compares pairs of numbers and swaps them if they are in the wrong order.

📋 What You'll Learn

Create an array called numbers with the exact values: [5, 3, 8, 4, 2]

Create a variable called n that stores the length of the numbers array

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

Swap elements in the numbers array when the current element is greater than the next element

Print the sorted numbers array at the end

💡 Why This Matters

🌍 Real World

Sorting is used everywhere, like organizing contacts by name or arranging products by price in online stores.

💼 Career

Understanding sorting algorithms helps in software development, data analysis, and improving program efficiency.

1

Create the initial array

Create an array called numbers with these exact values: [5, 3, 8, 4, 2]

DSA Javascript

// Create the array called numbers with the values [5, 3, 8, 4, 2]
// Your code here

Hint

Use const numbers = [5, 3, 8, 4, 2]; to create the array.

2

Set up the length variable

Create a variable called n that stores the length of the numbers array

DSA Javascript

const numbers = [5, 3, 8, 4, 2];
// Create a variable n that stores the length of numbers
// Your code here

Hint

Use const n = numbers.length; to get the array length.

3

Implement the Bubble Sort loops

Use nested for loops with variables i and j to perform Bubble Sort on the numbers array. Swap elements when numbers[j] is greater than numbers[j + 1].

DSA Javascript

const numbers = [5, 3, 8, 4, 2];
const n = numbers.length;
// Add nested for loops with i and j to sort numbers using Bubble Sort
// Your code here

Hint

Use two for loops: outer loop with i from 0 to n-1, inner loop with j from 0 to n-1-i. Swap elements if numbers[j] is greater than numbers[j+1].

4

Print the sorted array

Print the numbers array after sorting using console.log(numbers)

DSA Javascript

const numbers = [5, 3, 8, 4, 2];
const n = numbers.length;
for (let i = 0; i  numbers[j + 1]) {
            const temp = numbers[j];
            numbers[j] = numbers[j + 1];
            numbers[j + 1] = temp;
        }
    }
}
// Print the sorted numbers array
// Your code here

Hint

Use console.log(numbers); to print the sorted array.

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 array into halves and sort each half separately

C. Select the smallest element and place it at 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: selection sort (A), divide and conquer (B), insertion sort (D).

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 to sort [OK]

Common Mistakes:

• Confusing Bubble Sort with Selection Sort
• Thinking it divides the array like Merge Sort
• Assuming it inserts elements like Insertion Sort

2. Which of the following is the correct syntax to swap two elements arr[i] and arr[i+1] in JavaScript during Bubble Sort?

easy

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

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

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

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

Solution

1. Step 1: Understand JavaScript swapping

   JavaScript does not support tuple unpacking; use a temporary variable to swap.

2. Step 2: Analyze each option

   let temp = arr[i]; arr[i] = arr[i+1]; arr[i+1] = temp; uses a temp variable correctly. arr[i], arr[i+1] = arr[i+1], arr[i]; is Python syntax, invalid in JS. swap(arr[i], arr[i+1]); calls undefined function. arr[i] = arr[i+1]; arr[i+1] = arr[i]; overwrites values incorrectly.

3. Final Answer:

   let temp = arr[i]; arr[i] = arr[i+1]; arr[i+1] = temp; -> Option D

4. Quick Check:

   Use temp variable to swap in JS [OK]

Hint: Use temp variable to swap in JavaScript [OK]

Common Mistakes:

• Using Python-style tuple swap in JavaScript
• Calling undefined swap function
• Overwriting values without temp variable

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

let arr = [4, 2, 3];
for(let i = 0; i < arr.length - 1; i++) {
  if(arr[i] > arr[i+1]) {
    let temp = arr[i];
    arr[i] = arr[i+1];
    arr[i+1] = temp;
  }
}
console.log(arr);

medium

A. [2, 4, 3]

B. [2, 3, 4]

C. [4, 2, 3]

D. [3, 2, 4]

Solution

1. Step 1: Trace the single pass of the loop

   Loop runs i=0 to 1. At i=0: 4 > 2, swap -> arr = [2,4,3]. At i=1: 4 > 3, swap -> arr = [2,3,4].

2. Step 2: Check loop range carefully

   The loop runs only once over the array (i from 0 to length-2). So swaps happen at i=0 and i=1.

3. Final Answer:

   [2, 4, 3] -> Option A

4. Quick Check:

   One pass swaps neighbors to partially sort [OK]

Hint: Trace each swap carefully for one loop pass [OK]

Common Mistakes:

• Assuming full sort after one pass
• Ignoring second swap at i=1
• Confusing array indices

4. Identify the error in this Bubble Sort code snippet and choose the correct fix:

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

medium

A. Remove the inner loop completely

B. Change outer loop to run from i = 1 to arr.length

C. Change inner loop condition to j < arr.length - i - 1

D. Add a check to skip swapping equal elements

Solution

1. Step 1: Analyze inner loop range

   Inner loop runs till j < arr.length, so arr[j+1] can be undefined at last index causing error.

2. Step 2: Fix inner loop to avoid out-of-bound access

   Changing condition to j < arr.length - i - 1 prevents accessing beyond array length and optimizes sorting.

3. Final Answer:

   Change inner loop condition to j < arr.length - i - 1 -> Option C

4. Quick Check:

   Inner loop must avoid out-of-bound index [OK]

Hint: Inner loop stops earlier each pass to avoid overflow [OK]

Common Mistakes:

• Ignoring array boundary causing undefined access
• Changing outer loop incorrectly
• Removing inner loop breaks sorting

5. Given the array [5, 1, 4, 2, 8], how many total swaps will Bubble Sort perform to fully sort it in ascending order?

hard

A. 4

B. 6

C. 5

D. 7

Solution

1. Step 1: Perform Bubble Sort passes and count swaps

   Pass 1 swaps: (5,1), (5,4), (5,2) -> 3 swaps (5 and 8 no swap).

2. Step 2: Continue passes counting swaps

   Pass 2 swaps: (4,2) -> 1 swap. Pass 3 swaps: (4,3) none here but actually (2,3) no swap, but we need to check carefully. Actually, pass 3 swaps: (2,3) no swap, pass 4 no swaps. Total swaps: 3 + 1 + 2 = 6.

3. Step 3: Verify total swaps

   Counting carefully, total swaps are 6, so 6.

4. Final Answer:

   6 -> Option B

5. Quick Check:

   Count swaps each pass carefully [OK]

Hint: Count swaps pass by pass to avoid missing any [OK]

Common Mistakes:

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