排序算法比较

Question

I have a project, I need to test 3 sorting algorithms and find out which one of them are Insertion Sort, Bubble Sort, Selection Sort. I can't reach the methods so I test by using stopwatch in Java. I created 3 arrays.

int[] arr = new int[100000]; //This array is sorted
int[] randomarr = new int[100000]; //This array is random
int[] reversearr = new int[100000]; //This array is reversed

I tested these algorithms and here are my results :

- sort1 

 Sorted array took 11 seconds--Reversed array took 13 seconds--Random array took 24 seconds

- sort2

 Sorted array took 12 second--Reversed array took 12 seconds--Random array took 10 seconds

- sort3

 Sorted array took 1 millisecond--Reversed array took 12 seconds--Random array took 4 seconds

I am pretty sure sort3 is Insertion sort because it was faster than other ones in Sorted array. But I am confused about sort1 and sort2. Bubble sort has O(n) in its best case, Insertion sort also have O(n) in its best case but when I check my results, insertion sort best case is 1 millisecond so bubble sort's best case should be 1 millisecond too? How can I compare them ?

Answer 1

So you clearly have to work out which is which by means of examining the time taken to sort various arrays.

Here are some details on each of the algorithms (columns are best, average, worst, best space);

So you can quickly work out which one is selection sort by passing sorted lists of varying size to the algorithms, and seeing how long it takes. The one which acts quadratically, is selection sort .

Then, to decide between bubble sort and insertion sort , you'll need to read a little more deeply into how the algorithms work. bubble sort has an affectionately named issue; dinosaurs and turtles , which is, large elements at the beginning are quickly dealt with, but small elements at the end are inefficiently dealt with. You could then try profiling the two remaining algorithms ( bubble and insertion ) with sorted lists with the last element being the smallest, and see how they do. The one which performs better will be insertion sort.

If do exactly these tests on arrays of varying sizes, using just simple versions of these algorithms, i get the following:

so, based on the above info, i know that sort1 is bubble sort, sort3 is selection sort, and sort2 is insertion sort.