Bubble Sort Algorithm in DSA Javascript - Practice Problems & Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this Bubble Sort code?

Consider the following JavaScript code that sorts an array using Bubble Sort. What will be the printed output after running this code?

DSA Javascript

const arr = [5, 3, 8, 4, 2];
for (let i = 0; i < arr.length - 1; i++) {
  for (let j = 0; j < arr.length - 1 - i; j++) {
    if (arr[j] > arr[j + 1]) {
      const temp = arr[j];
      arr[j] = arr[j + 1];
      arr[j + 1] = temp;
    }
  }
}
console.log(arr.join(' -> ') + ' -> null');

A 5 -> 3 -> 8 -> 4 -> 2 -> null

B 2 -> 3 -> 4 -> 5 -> 8 -> null

C 8 -> 5 -> 4 -> 3 -> 2 -> null

D 2 -> 4 -> 3 -> 5 -> 8 -> null

💡 Hint

Remember Bubble Sort swaps adjacent elements if they are in the wrong order, pushing the largest to the end each pass.

Bubble Sort compares pairs and swaps them if needed, so the largest numbers move to the right. After all passes, the array is sorted ascending: 2, 3, 4, 5, 8.

🧠 Conceptual

intermediate

How many total swaps does Bubble Sort perform on this array?

Given the array [4, 2, 7, 3], how many swaps will Bubble Sort perform to sort it in ascending order?

A 6

B 4

C 3

D 5

💡 Hint

Count each time two adjacent elements are swapped during the sorting process.

Initial: [4,2,7,3] Pass 1: swap 4 and 2 → [2,4,7,3], swap 7 and 3 → [2,4,3,7] (2 swaps) Pass 2: swap 4 and 3 → [2,3,4,7] (1 swap) Pass 3: no swaps Total swaps = 3.

❓ Predict Output

advanced

What error does this Bubble Sort code produce?

Analyze the following Bubble Sort code snippet. What error will it raise when run?

DSA Javascript

const arr = [3, 1, 4];
for (let i = 0; i <= arr.length; i++) {
  for (let j = 0; j < arr.length - 1 - i; j++) {
    if (arr[j] > arr[j + 1]) {
      [arr[j], arr[j + 1]] = [arr[j + 1], arr[j]];
    }
  }
}
console.log(arr.join(' -> ') + ' -> null');

A No error, outputs: 1 -> 3 -> 4 -> null

B RangeError: Maximum call stack size exceeded

C TypeError: Cannot read property 'length' of undefined

D undefined -> undefined -> undefined -> null

💡 Hint

Check the loop conditions carefully for off-by-one errors causing undefined access.

The outer loop runs from i=0 to i=3 (arr.length=3). When i=3, inner loop j < -1 does not run. No invalid array access occurs. The array is sorted correctly to [1,3,4] with no error.

🔧 Debug

advanced

Identify the bug in this Bubble Sort implementation

This Bubble Sort code is intended to sort an array ascending but produces incorrect output. What is the bug?

DSA Javascript

const arr = [6, 2, 9, 1];
for (let i = 0; i < arr.length; i++) {
  for (let j = 0; j < arr.length - 1; j++) {
    if (arr[j] < arr[j + 1]) {
      const temp = arr[j];
      arr[j] = arr[j + 1];
      arr[j + 1] = temp;
    }
  }
}
console.log(arr.join(' -> ') + ' -> null');

A The outer loop should run from arr.length - 1 down to 0

B The inner loop should run fewer times each pass to avoid unnecessary comparisons

C The temporary variable is not used correctly causing wrong swaps

D The comparison operator should be '>' to sort ascending, not '<'

💡 Hint

Check the comparison direction to see if it sorts ascending or descending.

The code uses 'arr[j] < arr[j + 1]' which swaps if left is less than right, causing descending order. To sort ascending, it should be 'arr[j] > arr[j + 1]'.

🚀 Application

expert

How many passes does Bubble Sort need to sort this array?

Given the array [1, 2, 3, 4, 5], how many passes (outer loop iterations) will Bubble Sort perform before it stops if optimized to stop early when no swaps occur?

DSA Javascript

const arr = [1, 2, 3, 4, 5];
let n = arr.length;
for (let i = 0; i < n; i++) {
  let swapped = false;
  for (let j = 0; j < n - 1 - i; j++) {
    if (arr[j] > arr[j + 1]) {
      [arr[j], arr[j + 1]] = [arr[j + 1], arr[j]];
      swapped = true;
    }
  }
  if (!swapped) break;
}
console.log(arr.join(' -> ') + ' -> null');

A 1

B 4

C 5

D 0

💡 Hint

If the array is already sorted, the algorithm stops after the first pass with no swaps.

Since the array is already sorted, no swaps happen in the first pass, so the loop breaks immediately after 1 pass.