AlexETay7 / Hashing-Experiments

An experiment that studies how a hash table's load factor α affects the average number of probes required using linear probing and double hashing for various types of inputs.

Project #3: Experiments with Hashing

• Author: Alex Taylor
• University Project

Overview

In this project I implemented a non-generic Hashtable class with open addressing. This project studies how the load factor affects the average number of probes required using linear probing and double hashing for various types of inputs.

Reflection

This project was pretty challenging at first becuase I did not feel like I got a super good grip on the concept in lecture. What worked well for me was going through the lecture notes and the textbook and familiarizing myself with the problem this code was solving and WHY this method is worth using. Once I understood how classes were supposed to interact with one another, I was able to implement most of them without too much trouble.

I enjoyed making the HashtableExperiment class for the most part, however some of the condition checking was a little confusing. It was a lot of fun running the project on AWS! The only thing I struggled with was realizing I needed a personal access token in order to clone my github repo to my EC2 instance. Overall I definitely have a better grasp on linear probing and double hashing, and enjoyed this project!

Compiling and Using

Experiments are done via the HashtableExperiment.java file.

Compile this class by doing:

javac HashtableExperiment.java

Run this command to get a prompt of how to use the class:

java HashtableExperiment

Note that doing "java HashtableExperiment.java" here will cause an error

Console output will give results once the program finishes.

Results

Data Source 1 - Integer Objects

Load Factor	Collision Strategy	Hash Table Size	Inserted Elements	Duplicates	Average Probes
0.5	Linear Probing	47896	47896	0	1.51
0.5	Double Hashing	47896	47896	0	1.39
0.6	Linear Probing	57475	57475	0	1.75
0.6	Double Hashing	57475	57475	0	1.53
0.7	Linear Probing	67054	67055	1	2.17
0.7	Double Hashing	67054	67055	1	1.72
0.8	Linear Probing	76633	76634	1	2.98
0.8	Double Hashing	76633	76634	1	2.01
0.9	Linear Probing	86212	86214	2	5.46
0.9	Double Hashing	86212	86214	2	2.57
0.95	Linear Probing	91002	91002	0	10.52
0.95	Double Hashing	91002	91002	0	3.13
0.99	Linear Probing	94834	94835	1	50.02
0.99	Double Hashing	94834	94835	1	4.66

Data Source 2 - Dates as longs

Load Factor	Collision Strategy	Hash Table Size	Inserted Elements	Duplicates	Average Probes
0.5	Linear Probing	47896	47896	0	1.08
0.5	Double Hashing	47896	47896	0	1.11
0.6	Linear Probing	57475	57475	0	1.08
0.6	Double Hashing	57475	57475	0	1.14
0.7	Linear Probing	67054	67054	0	1.10
0.7	Double Hashing	67054	67054	0	1.20
0.8	Linear Probing	76633	76633	0	1.22
0.8	Double Hashing	76633	76633	0	1.37
0.9	Linear Probing	86212	86212	0	1.76
0.9	Double Hashing	86212	86212	0	2.21
0.95	Linear Probing	91002	91002	0	2.18
0.95	Double Hashing	91002	91002	0	2.87
0.99	Linear Probing	94834	94834	0	3.71
0.99	Double Hashing	94834	94834	0	4.31

Data Source 3 - String Objects

Load Factor	Collision Strategy	Hash Table Size	Inserted Elements	Duplicates	Average Probes
0.5	Linear Probing	47896	1305930	1258034	1.60
0.5	Double Hashing	47896	1305930	1258034	1.39
0.6	Linear Probing	57475	1587659	1530184	2.15
0.6	Double Hashing	57475	1587659	1530184	1.53
0.7	Linear Probing	67054	1869206	1802152	3.60
0.7	Double Hashing	67054	1869206	1802152	1.72
0.8	Linear Probing	76633	2147748	2071115	6.71
0.8	Double Hashing	76633	2147748	2071115	2.02
0.9	Linear Probing	86212	2840050	2753838	19.81
0.9	Double Hashing	86212	2840050	2753838	2.57
0.95	Linear Probing	91002	3013622	2922620	110.59
0.95	Double Hashing	91002	3013622	2922620	3.19
0.99	Linear Probing	94834	3024134	2929300	471.67
0.99	Double Hashing	94834	3024134	2929300	4.70

Sources used

• Algorithms Class Notes
• Algorithms Textbook
• Tutoring Center

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