Bubble Sort Algorithm Lecture Notes

Overview

Purpose: Understanding Bubble Sort and its application in sorting data for exams.
Goals:
- Understand main steps of Bubble Sort.
- Identify and apply the algorithm.
- Trace and write the code for Bubble Sort.
- Recognize Bubble Sort when given a piece of code.

Bubble Sort Basics

Definition: Orders an unordered list by comparing each item with the next and swapping if out of order.
Termination: The algorithm ends when no more swaps are needed.
Performance: Inefficient but easy to implement, ideal for small datasets.
Use Case: Simple sorting needs.

Steps in Bubble Sort

Initialize Variables:
- n tracks the range of elements to check (initially set to the length of the dataset).
- swapped flag indicates if a swap has occurred (initially set to true).
While Loop: Runs until n > 0 and swapped is true.
- Inside the Loop:
  - Set swapped to false.
  - Decrement n by 1 each iteration.
  - For Loop: Iterates through the subset of elements (0 to n-1).
    - Compare current item with next item.
    - Swap if out of order and set swapped to true.
Repeat until no swaps are needed and the entire list is sorted.

Pseudocode

n = length(items)
swapped = true
while n > 0 and swapped == true
  swapped = false
  n = n - 1
  for index in range(0 to n-1)
    if items[index] > items[index + 1]
      swap(items[index], items[index + 1])
      swapped = true

Python Implementation

Example: items = ['Florida', 'Georgia', 'Delaware', 'Alabama', 'California'] n = len(items) swapped = True while n > 0 and swapped: swapped = False n -= 1 for i in range(n): if items[i] > items[i + 1]: temp = items[i] items[i] = items[i + 1] items[i + 1] = temp swapped = True print(items)
Explanation: Step-by-step sorting breaks down the problem and swaps items until the list's largest elements bubble up to their correct position.

Key Points to Remember

Multiple ways to implement bubble sort (variants may exist).
Data structures may be zero-indexed or one-indexed depending on the programming language.
Bubble sort can be optimized, e.g., using a cocktail sort (bidirectional pass).
Thorough understanding of bubble sort includes being able to trace it on paper and code it in a language of your choice.

Additional Resources

Essential Algorithms for A-Level Computer Science: A book covering data structures and algorithms in detail, available on Amazon.