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    <p>“As I expect the file to be large, I did not use a HashMap to store the lines but opted instead for a String array.”</p> <p>I don’t agree with your reasoning; the larger the file, the more of a performance benefit you’ll get from hashing. In your code, you’re comparing each lines with <em>all</em> succeeding lines, requiring O(n²) computational complexity for the whole file.</p> <p>On the other hand, if you were to use an efficient hashing algorithm, then each hash lookup would complete in O(1); the computational complexity of processing your entire file becomes O(n).</p> <p>Try using a <code>HashSet&lt;string&gt;</code> and observe the difference in the processing time:</p> <pre><code>public static void RemoveDuplicateEntriesinFile(string filepath) { if (filepath == null) throw new ArgumentException("Please provide a valid FilePath"); HashSet&lt;string&gt; hashSet = new HashSet&lt;string&gt;(File.ReadLines(filepath)); File.WriteAllLines(filepath, hashSet); } </code></pre> <p><strong>Edit</strong>: Could you try the following version of the algorithm and check how long it takes? It’s optimized to minimize memory consumption:</p> <pre><code>HashAlgorithm hashAlgorithm = new SHA256Managed(); HashSet&lt;string&gt; hashSet = new HashSet&lt;string&gt;(); string tempFilePath = filepath + ".tmp"; using (var fs = new FileStream(tempFilePath, FileMode.Create, FileAccess.Write)) using (var sw = new StreamWriter(fs)) { foreach (string line in File.ReadLines(filepath)) { byte[] lineBytes = Encoding.UTF8.GetBytes(line); byte[] hashBytes = hashAlgorithm.ComputeHash(lineBytes); string hash = Convert.ToBase64String(hashBytes); if (hashSet.Add(hash)) sw.WriteLine(line); } } File.Delete(filepath); File.Move(tempFilePath, filepath); </code></pre>
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    1. COI am currently running the code to find out how much better than mine it is. :)
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    2. COTurns out the above is not so much better than mine really. I tested it and it came back with Time Elapsed = 32.14.838245. Approximately the same time as my original code really. Any Ideas how I can make it even faster?
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    3. COHow many characters does each line have?
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