Fundamentals of Computer Science I (CS151.02 2007S)
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This homework assignment is also available in PDF.
Assigned: Tuesday, April 24, 2007
Due: Friday, April 27, 2007
No extensions!
Summary: In this assignment, you will explore another sorting algorithm, selection sort.
Purpose: To help you think more about sorting.
Expected Time: One to two hours.
Collaboration: You may work in a group of any size between one and four, inclusive. You may consult others outside your group, provided you cite those others. You need only submit one assignment per group.
Submitting: Email me your work, using a subject of CSC151 Homework 16.
Warning: So that this exercise is a learning assignment for everyone, I may spend class time publicly critiquing your work.
As you may recall from our inclass discussion of sorting techniques, one popular strategy for sorting vectors involves repeatedly finding the smallest remaining value and then swapping it into the next place in the vector. We call this procedure selection sort because the primary operation is selecting the smallest value.
The process is fairly straightforward. For example, in a vector of 10 elements, selection sort
As that example suggests, a key helper for selection sort is finding the index of the smallest value in a subvector. We might document that procedure as follows:
;;; Procedure: ;;; indexofsmallest ;;; Parameters: ;;; vec, a vector ;;; pos, an integer ;;; mayprecede?, a binary predicate ;;; Purpose: ;;; Find the index of the smallest value in positions [pos..len) of vec. ;;; Produces: ;;; ios, an integer ;;; Preconditions: ;;; mayprecede? is transitive and reflexive. ;;; 0 <= pos < (vectorlength vec). ;;; vec contains no duplicate values. ;;; Postconditions: ;;; For all i, pos <= i < (vectorlength vec), i not equal to ios, ;;; (mayprecede? (vectorref vec ios) (vectorref vec i)).
a. Implement indexofsmallest
.
b. Implement (swap! vec i j)
, a procedure that swaps
the values at positions i
and j
of
vec
.
c. Using indexofsmallest
and swap!
,
implement selectionsort!
. Note that you will probably
want to iterate over the position in the vector.
Sunday, 12 November 2006 [Samuel A. Rebelsky]
Monday, 13 November 2006 [Samuel A. Rebelsky]
indexofsmallest
.
Monday, 23 April 2007 [Samuel A. Rebelsky]
[Skip to Body]
Primary:
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[Academic Honesty]
[Instructions]
Current:
[Outline]
[EBoard]
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[Assignment]
Groupings:
[EBoards]
[Examples]
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[Labs]
[Outlines]
[Projects]
[Readings]
Reference:
[Scheme Report (R5RS)]
[Scheme Reference]
[DrScheme Manual]
Related Courses:
[CSC151 2006F (Rebelsky)]
[CSC151.01 2007S (Davis)]
[CSCS151 2005S (Stone)]
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