🧋 Bubble Sort Bubble Sort Definition Inefficient version Most Efficient version Questions Good Revision Materials Got some paper flashcards too Bubble Sort https://youtu.be/lyZQPjUT5B4 Definition Sorting items in an array in ascending order by doing lots of comparisons and swaps Bubble Sort 1 Inefficient version Just to understand the mechanics #setting up array a=[15,16,6,8,5] n = len(a) for i in range(n-1): for j in range(n-1): if a[j]> a[j+1]: temp = a[j] a[j] = a[j+1] a[j+1] = temp #end if #end for #end for print(a) #instead of doing temp = a[j]; a[j] = a[j+1]; a[j+1] = temp, you could do: #a[j],a[j+1] = a[j+1],a[j] 💡 Things to remember about this bubble sort The outer loop to deal with passes Inner loop to deal with comparisons After the first pass the biggest number should be on the right hand side If not specified, assume the sort is always in the in ascending order Even once the array is sorted, the code will continue to sort through/make comparisons in the array during the last pass - quite inefficient Even if the array is ordered after 1 pass, it will still continue to sort through n-1 passes. Imagine having n= 100 Most Efficient version #setting up array a=[15,16,6,8,5] Bubble Sort 2 n = len(a) for i in range(n-1): flag=0 #boolean flag = false for j in range(n-1-i): #(n-j-i) number of comparisons reduced by i with each iteration because after each pass, #the items that have been sorted to their correct position don't need to be compared again if a[j]> a[j+1]: temp = a[j] a[j] = a[j+1] a[j+1] = temp #if this code has been executed, then swapping has occured and the array is unordered #flag = true and the loop will continue flag = 1 #end if #end for if flag ==0: # if flag remains false, then the swapping code hasn't been carried out #it means that the array is sorted and the loop is broken break #end if #end for print(a) 💡 Tips Some languages start indexes from 1 instead of 0, watch out in SQA, otherwise marks will be lost If not specified, use the efficient bubble sort Questions How does a bubble sort operate? SQA 2008 MI compares adjacent items[1] if out of order swaps them[1] Bubble Sort 3 repeats until there are no more swaps[1] This is what I wrote “ Starting from index 0, the bubble sort compares 2 items in adjacent indexes to each other and swaps them if a preset condition is met This comparison repeats until the desired number is in the correct position This process repeats until there are no more swaps What does the outer loop of a bubble sort deal with? The number of passes What does the inner loop of a bubble sort deal with? The number of comparisons If not specified, what order should the bubble sort resort to? Ascending Order Why is the bubble loop with 2 fixed loops inefficient? Even once the array is sorted, the code will continue to sort through/make comparisons in the array during the last pass Disadvantage of Bubble Sort? Used quadratic time, if the list increases, then the time taken to execute will increase a ton How to make Bubble Sort more efficient? Use a Boolean variable The space complexity for a bubble sort is O(1), because only a single additional memory space is required i.e. for the temp variable Bubble Sort 4 💡 Bubble Sort Summary Definition: The process of sorting an unordered list by comparing adjacent values, swapping if out of order and repeating until there are no more swaps Good Revision Materials Got some paper flashcards too https://quizlet.com/gb/747674545/bubble-sort-flash-cards/?new Bubble sort - Introducing algorithms - GCSE Computer Science Revision - BBC Bitesize An example of a computer is bubble sort . This is a simple algorithm used for taking a list of jumbled up numbers and putting them into the correct order. The algorithm runs as follows: Look at the first number in the list. Compare the current number with the next number. https://www.bbc.co.uk/bitesize/guides/z22wwmn/revision/3 AH Computing Revision - Bubble Sort What is a Bubble Sort? https://sites.google.com/rgc.aberdeen.sch.uk/rgcahcomputingrevi sion/software-design/standard-algorithms/bubble-sort http://www.bbc.co.uk/bitesize/guides/z22wwmn/revision/3 AH Computing Revision - Bubble Sort What is a Bubble Sort? http://sites.google.com/rgc.aberdeen.sch.uk/rgcahcomputingrevisi on/software-design/standard-algorithms/bubble-sort Bubble Sort 5 Run n 1 0 j 2 Bubble Sort 6
