Standard Sorting Algorithms (Edexcel GCSE Computer Science)

What is a sorting algorithm?

• Sorting algorithms are precise step-by-step instructions that a computer can follow to efficiently sort data in massive datasets

• Three common sorting algorithms are:

  • Bubble sort

  • Merge sort

Bubble Sort

What is a bubble sort?

• A bubble sort is a simple sorting algorithm that starts at the beginning of a dataset and checks values in 'pairs' and swaps them if they are not in the correct order

• One full run of comparisons from beginning to end is called a 'pass', a bubble sort may require multiple 'passes' to sort the dataset

• The algorithm is finished when there are no more swaps to make

How do you perform a bubble sort?

Example

• Perform a bubble sort on the following dataset

A bubble sort in python

• In the exam, students are required to understand the mechanics of the algorithm as well as the advantages and disadvantages of it

• Students are not required to remember the code for the algorithm

# unsorted dataset
nums=[66, 7, 69, 50, 42, 80, 71, 321, 67, 8, 39]

# count the length of the dataset
numlength = len(nums)

# sets a flag to initiate the loop
swaps = True

while swaps == True : 
    swaps = False
    # loop through the dataset
    for y in range(numlength-1) :
        # if the first number is bigger than the second number
        if nums[y] > nums[y+1] :
            # swap the numbers using a temporary variable
            temp = nums[y]
            nums[y] = nums[y+1]
            nums[y+1] = temp
            # sets the flag to true
            swaps = True

# prints the sorted list
print (nums)

Merge Sort

What is a merge sort?

• A merge sort is a sorting algorithm that uses the 'divide and conquer' strategy of dividing a dataset into smaller sub-datasets and merging them back together in the correct order

How do you perform a merge sort?

Example

• Perform a merge sort on the following dataset

• The code for a merge sort is complex and not necessary for the exam

• In the exam students are only expected to be able to follow the steps and illustrate the algorithm, not code it