CS 420/222   Fall 1998,  Instructor:  Jeffrey Horn 

HOMEWORK 3:  POINTERS and CLOSED HASHING
 

Handed out/Assigned:	Friday, October 9, 1998
Due:	Wednesday, Oct. 21, 1998

OVERALL:  The problem setting is as described in class:  you are to maintain a history of all binary chromosomes seen so far.  But this time, we will work with arrays of pointers, rather than arrays of individuals themselves.  Furthermore, we will implement a hash table, so that we can try to get O(1) member checks!  (as compared to O(lg N) lookup times for binary search).

WHAT TO HAND IN:  Hand-in the code, both hardcopy and sending me the ascii text file by email to jhorn@nmu.edu.  And DO comment!  (I always find it easier to go back and add comments later, but whatever works for you.  See my style of commenting.  At the very least, comment modules such as classes, methods, and functions, that you write or modify.)   Also, answer the questions below and email me the text file with answers, or turn in hardcopy to my mailbox or to me in class.

PURPOSE:  To learn the use of pointers in C++, and to implement hashing.

SPECIFICS:

THE CODE:  (you can go directly to the files by clicking here)

 Here is the definition for an individual, in "individual.h":
 

class Individual{

      private:

      protected:

      public:

         Individual() {};                     // Constructor.  nothing here for now.
         boolean chromosome[CHROMLENGTH];     // Chrom is a string of true, false.
         int generation_first_seen;           // useful field for later use.
         float fitness;                       // Each chromosome has a fitness.
         boolean equal(Individual other);     // Compare other chromosome to oneself.
         boolean greater(Individual other);   // Compare other chromosome to oneself.
         void printchrom();                   // Print chromosome to console.

};

Similary, the file "sortedarray.h"  contains the interface for the class sortedarray (of individuals), while "sortedarray.cc contains implementations for those methods.

The file "main.cc" creates an object (Pool) of class sortedarray, while "input" contains the actual chromosomes to be loaded into the sortedarray upon creation.
 

WHAT TO DO:

(0)  Download all six of these files into your own directory.

(I)  Rewrite the "member" and "IndexOf" methods of the SortedArray class so that they implement a binary search of the array of individuals, rather than the linear search they use now.  You can assume the array is sorted!  Test your code  (I will!)  I suggest you leave member and IndexOf intact, and write two new methods with slightly different names.  You might be able to use the old methods in your testing.

(II)  Implement a new method for SortedArray, called "printFirst()"  which simply prints the chromosome of the first individual in the array, assuming there is one.

(III)  Add code to count the number of chromosome comparisons made during a "member" check or "where" check.  In other words, count the number of times "individual.greater" or "individual.equal" are called (i.e., both count as comparisons).   Make methods that print this count (e.g., maybe a different version of "member", like "count_member", that does the member check and also prints the count.  There are many ways to do this.  Think about where is the most logical place to put the counter code.  Which object should track this?  After you get this working, find an example to show that your binary search is faster than the linear search (i.e., give me a chromosome to search for, then the counts from both binary search and linear search).  EXTRA CREDIT:  find an example where the linear search is faster!  (and give the counts, so we can see how MUCH faster it is)

(IV)  What is the run-time complexity of the method "sortedarray::printall()"?  Just give Big Oh notation, and assume two measures of input size:  N (the number of chromosomes in the array) and L, the length of the chromosomes in bits.  In our example input file, N=37 and L=8.  As a basic computer operation, count each iteration through any loop.