Computer Science Fundamentals (CS153 2003S)

Lab: Sorting

Summary: In this lab, we explore a variety of issues related to sorting.



Exercise 0: Preparation

a. Start DrScheme.

b. Copy the code from the accompanying reading into DrScheme.

Exercise 1: Testing Insert

a. Test both versions of the insert-number procedure from the reading by inserting a number

b. What happens if ls is not in ascending order when insert-number is invoked?

Exercise 2: Inserting Strings

Write a new insert-string procedure that inserts a string into a list of strings that are in alphabetical order:

> (insert-string "dog" (list "ape" "bear" "cat" "emu" "frog"))
("ape" "bear" "cat" "dog" "emu" "frog")

In case you've forgotten, string<? and string-ci<? are useful predicates for comparing strings for order.

Exercise 3: Generalizing Insertion

a. Show how to call the generalized insert procedure using lists of strings.

b. Show how to call the generalized insert procedure using lists of numbers.

c. Redefine insert-number so that it uses insert

d. Document insert.

Exercise 4: Displaying Steps in Insertion Sort

a. Add calls to the display and newline procedures to the body of the helper in insertion-sort-numbers so that it displays the values of unsorted and sorted, appropriately labeled, at each step of the sorting process.

b. Use the revised insertion-sort-numbers procedure to sort the values 7, 6, 12, 4, 10, 8, 5, and 1.

Exercise 5: Checking Potential Problems

Test the insertion-sort-numbers procedure on some potentially troublesome arguments:

Exercise 6: Estimating Running Times

Using time, determine how long it takes to insertion sort lists for 50, 100, 150, and 200 numbers. You should probably try a few different lists of each size. If you find that these examples are too quick, use larger lists.

You may want to use the following procedure to generate your lists.

;;; Procedure:
;;;   random-list
;;; Parameters:
;;;   max, the largest value to be produced
;;;   len, an integer
;;; Purpose:
;;;   Produces a list of "random" values.
;;; Produces:
;;;   random-values
;;; Preconditions:
;;;   max > 0
;;;   len >= 0
;;; Postconditions:
;;;   random-values has length len.
;;;   Every value in random-values is between 0 and max, inclusive.
;;;   The result list is hard to predict.
(define random-list
  (lambda (max len)
    (if (= len 0) null
        (cons (random (+ max 1)) (random-list max (- len 1))))))

Exercise 7: Generalizing Insertion Sort

Document, write, and test a procedure, (insertion-sort list may-precede?). that generalizes the insertion-sort-numbers procedure.

Exercise 8: Inserting into Vectors

Document, write, and test the generalized insert! procedure to insert into a sorted vector. Your procedure should take the following parameters:

Your procedure should shift values as appropriate to make space for the new value. Your procedure should not affect values in the vector after space-pos.

You can assume that the value to be inserted belongs before space-pos.

Hint: Work backwards from space-pos.

Exercise 9: Testing Vector-Based Insertion Sort

Create and name a vector containing the strings "bear", "emu", "frog", "ape", "dog", and "cat".

Rearrange the elements of the vector into alphabetical order by means of an appropriate call to insertion-sort!. (Note that the sorting occurs as a side effect of this call. Hence, to confirm that the sorting procedure worked you'll have to inspect the vector again afterwards.)




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Samuel A. Rebelsky,