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POBuild trie faster
 

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    <p>I'm making an mobile app which needs thousands of fast string lookups and prefix checks. To speed this up, I made a Trie out of my word list, which has about 180,000 words. </p> <p>Everything's great, but the only problem is that building this huge trie (it has about 400,000 nodes) takes about <strong>10 seconds</strong> currently on my phone, which is really slow.</p> <p>Here's the code that builds the trie.</p> <pre><code>public SimpleTrie makeTrie(String file) throws Exception { String line; SimpleTrie trie = new SimpleTrie(); BufferedReader br = new BufferedReader(new FileReader(file)); while( (line = br.readLine()) != null) { trie.insert(line); } br.close(); return trie; } </code></pre> <p>The <code>insert</code> method which runs on <code>O(length of key)</code></p> <pre><code>public void insert(String key) { TrieNode crawler = root; for(int level=0 ; level &lt; key.length() ; level++) { int index = key.charAt(level) - 'A'; if(crawler.children[index] == null) { crawler.children[index] = getNode(); } crawler = crawler.children[index]; } crawler.valid = true; } </code></pre> <p>I'm looking for intuitive methods to build the trie faster. Maybe I build the trie just once on my laptop, store it somehow to the disk, and load it from a file in the phone? But I don't know how to implement this.</p> <p>Or are there any other prefix data structures which will take less time to build, but have similar lookup time complexity?</p> <p>Any suggestions are appreciated. Thanks in advance.</p> <p><strong>EDIT</strong></p> <p>Someone suggested using Java Serialization. I tried it, but it was <strong>very</strong> slow with this code:</p> <pre><code>public void serializeTrie(SimpleTrie trie, String file) { try { ObjectOutput out = new ObjectOutputStream(new BufferedOutputStream(new FileOutputStream(file))); out.writeObject(trie); out.close(); } catch (IOException e) { e.printStackTrace(); } } public SimpleTrie deserializeTrie(String file) { try { ObjectInput in = new ObjectInputStream(new BufferedInputStream(new FileInputStream(file))); SimpleTrie trie = (SimpleTrie)in.readObject(); in.close(); return trie; } catch (IOException | ClassNotFoundException e) { e.printStackTrace(); return null; } } </code></pre> <p>Can this above code be made faster?</p> <p>My trie: <a href="http://pastebin.com/QkFisi09" rel="noreferrer">http://pastebin.com/QkFisi09</a></p> <p>Word list: <a href="http://www.isc.ro/lists/twl06.zip" rel="noreferrer">http://www.isc.ro/lists/twl06.zip</a></p> <p>Android IDE used to run code: <a href="http://play.google.com/store/apps/details?id=com.jimmychen.app.sand" rel="noreferrer">http://play.google.com/store/apps/details?id=com.jimmychen.app.sand</a></p>
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    1. USBruce
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    1. COI cannot install the ide on an android gingerbread?
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    2. COI would suggest to start from profiling. At least measuring which part is spent for (1) reading from file, (2) finding location in trie and (3) creating a new node
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    3. CO@Bruce Did you ever try the binary search technique? I saw good results with it.
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      1. USJustin
 

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