Sorting

















What's Sorting?



Why is Sorting Important?


	1. people can process data better when it is sorted

		words in a dictionary
		index of a book


	2. some algorithms are faster when the input is sorted

		binary search
		finding duplicates

















Selection Sort (10.2)

















How does Selection Sort work?

	keep a mark between the sorted and unsorted parts
	the sorted part starts empty

	find the smallest item in the unsorted part
	swap it with the first item in the unsorted part

	move the mark one place and repeat



Show each step of Selection Sort on the List.

	5 4 3 1 2

















Classwork
You may work with a partner.

Show each step of Selection Sort on the List.

	5 2 7 3 4

















Selection Sort Code

    for each i from 0 to size-2

	min = i
	for each j from i+1 to size-1
	    if list[j] < list[min]
	       min = j

	swap list[i] and list[min]

    end


What's the running time for Selection Sort?

Does the running time for Selection Sort depend on
the kind of input you give it?


DEMO	(selection sort on sorted, reverse, random data)

















Insertion Sort (10.4)

















How does Insertion Sort work?

	keep a mark between the sorted and unsorted parts
	the sorted part starts with the first item

	remove the first item from the unsorted part
	insert it into the sorted part

	move the mark one place and repeat



Show each step of Insertion Sort on the List.

	5 2 7 3 4

















Classwork
You may work with a partner.

Show each step of Insertion Sort on the List.

	8 5 2 7 3

















Insertion Sort Code

  for each i from 1 to size-1

    j = i
    item = list[j]

    while j > 0 and list[j-1] > item
      list[j] = list[j-1];
      j--;
    end while

    list[j] = item

  end for


What's the running time for Insertion Sort?

Does the running time for Insertion Sort depend on
the kind of input you give it?

What kind of input is worst-case for Insertion Sort?

What kind of input is best-case for Insertion Sort?

How does Insertion Sort perform on random input?


DEMO	(insertion sort on sorted, reverse, random data)