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AndrewTrieu
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<html>
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<head>
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<title>Task description: Open Hashing</title>
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<meta charset="utf-8">
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</head>
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<body>
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<div>
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<h4>1. Implementing the Hash Table</h4>
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</div>
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<div>Create your own hash table that uses open hashing in Python. Each slot of the hash table contains a linked
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structure where the data (keys) are stored. The hash system must include search, insert, and delete operations. The hash table must be able to store both integer (<em>int</em>)
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and string (<em>str</em>) values. That means that also all the operations/methods (search, insert, and delete) need to work with both data types. You can decide or design the hash function by yourself.<br></div>
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<br>
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<div>Consider following things when you are creating the hash table:</div>
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<ul>
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<ul>
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<li>The size of the hash table is <strong>fixed</strong>. That means that after initializing the size of the table must stay the same.</li><li>You must implement the linked structure where the data is stored by yourself.<br></li><li>Choose your hashing function wisely because it must work efficiently with very large hash tables.
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A Good start is the string folding. Be as creative you want but be prepared to explain how it works!</li>
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<li>Document your code!</li>
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</ul>
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</ul>
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<div><div>Save the code of your new data structure as <strong>hash_1.py</strong></div><br></div><div>Answer to the following essay questions:</div>
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<ol>
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<li>Present the structure of your hash table.</li>
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<li>What hashing function did you choose and why?</li>
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<li>What (including required) methods your hash table has and explain briefly how do they work?</li>
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</ol><br>
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<div>
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<h4>2. Testing and Analyzing the Hash Table</h4>
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</div>
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<div>Create a Python program: <strong>hash_2.py</strong>:</div>
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<ol>
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<li>Create a new hash table of size \(3\). Add items <strong>12, 'hashtable', 1234, 4328989, 'BM40A1500', -12456, 'aaaabbbbcccc'</strong>
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to the hash table. Present the structure of the hash table each time when a new value is added.</li>
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<li>Now try to find values <strong>-12456, 'hashtable', 1235</strong>. Print out the results.</li>
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<li>Remove values <strong>'BM40A1500', 1234, 'aaaabbbbcccc'</strong>. Present the final structure of the hash table.</li>
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</ol>
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<div>Answer to the following essay questions:</div>
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<ol>
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<li>What is the running time of adding a new value in your hash table and why?</li>
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<li>What is the running time of finding a new value in your hash table and why?</li>
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<li>What is the running time of removing a new value in your hash table and why?</li>
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</ol>
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<div>Use \(\Theta\) notation. Consider what factors influence the running time of the methods.</div>
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<br>
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<br>
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<div>
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<h4>3. The Pressure Test</h4>
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</div>
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<div>Let's put the hash table in a real use. The text file <a href="data/words_alpha.txt"><em>words_alpha.txt</em></a> (source: https://github.com/dwyl/english-words/)
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contains \(370105\) English (and not so English) words. The text file
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<a href="data/kaikkisanat.txt"><em>kaikkisanat.txt</em></a> (source: https://github.com/hugovk/everyfinnishword) contains \(93086\) Finnish words. Your task is to find all words from <em>kaikkisanat.txt</em> that are also in <em>words_alpha.txt</em> (exact matches).
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</div>
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<br>
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<div>Create a new Python file <strong>hash_3_1.py</strong>:</div>
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<ol>
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<li>Create a new hash table of size \(10000\).</li>
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<li>Read all words from <em>words_alpha.txt</em> and store them to your hash table.</li>
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<li>While reading words from <em>kaikkisanat.txt</em> check how many of them can you find from the hash table
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and print out the final result.</li>
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</ol>
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<div>Measure the runtime for each step. Tabulate the results
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as follows:
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</div>
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<br>
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<table frame="grey" cellspacing="1" cellpadding="0" border="1">
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<tbody>
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<tr>
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<th>Process</th>
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<th>Time (s)</th>
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</tr>
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<tr>
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<td>Initializing the hash table</td>
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<td></td>
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</tr>
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<tr>
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<td>Adding the words</td>
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<td></td>
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</tr>
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<tr>
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<td>Finding the common words</td>
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<td></td>
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</tr>
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</tbody>
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</table>
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<br>
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<div>How does your hash table stand against a linear array? Repeat the previous test,
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but this time store the words from <em>words_alpha.txt</em> to a <em>list</em> instead of the hash table. Save your code as <strong>hash_3_2.py</strong><br></div>
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<div><br></div><div>Answer to the following essay questions:</div>
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<ol>
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<li>Which data structure was faster in adding the words from the file and why?</li>
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<li>In which data structure was the search faster and why?</li>
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<li>Are you able to make the test program in <strong>hash_3_1.py</strong> faster (even slight improvements)?
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<ul>
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<li>Try to change the size of the hash table.</li>
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<li>How well is the data distributed in the hash table?</li>
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</ul>
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</li>
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</ol>
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<br>
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<p>Provide your answers to all the essay questions in a single PDF file. You can use the template below:</p><a href="data/PA_essay_template.odt?time=1665307225135">
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</a><p><a href="data/PA_essay_template.odt?time=1665398460962">PA_essay_template.odt</a><br></p>
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</body>
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</html>
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