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POIdentifying duplicate elements in a list containing 300k+ Strings
 

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  1. POIdentifying duplicate elements in a list containing 300k+ Strings
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    <p>I have a list containing 305899 Strings (which is the username for a website). After I remove all the duplicates, the number goes down to 172123 Strings.</p> <p>I want to find how many times a particular String (the username) is repeated in that ArrayList. I wrote a simple bubble sort type logic but it was too slow. </p> <pre><code>private static Map&lt;String, Integer&gt; findNumberOfPosts(List&lt;String&gt; userNameList) { Map&lt;String, Integer&gt; numberOfPosts = new HashMap&lt;String, Integer&gt;(); int duplicate = 0; int size = userNameList.size(); for (int i = 0; i &lt; size - 1; i++) { duplicate = 0; for (int j = i + 1; j &lt; size; j++) { if (userNameList.get(i).equals(userNameList.get(j))) { duplicate++; userNameList.remove(j); j--; size--; } } numberOfPosts.put(userNameList.get(i), duplicate); } return numberOfPosts; } </code></pre> <p>Then I changed it to this:</p> <pre><code>private static Map&lt;String, Integer&gt; findNumberOfPosts(List&lt;String&gt; userNameList) { Map&lt;String, Integer&gt; numberOfPosts = new HashMap&lt;String, Integer&gt;(); Set&lt;String&gt; unique = new HashSet&lt;String&gt;(userNameList); for (String key : unique) { numberOfPosts.put(key, Collections.frequency(userNameList, key)); } return numberOfPosts; } </code></pre> <p>This was really slow as well. When I mean slow, it would take like 30+ minutes to through the list. </p> <p>Is there any other efficient way to handle this problem? Just reduce the time it takes to find and count duplicate elements?</p>
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    1. COCan a two have the same username, why duplicates??
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      1. USNoor
    2. CO"I wrote a simple bubble sort type logic but it was too slow." - yeah, that's the problem with Bubble Sort: it's pathelogical O(N^2) will get you every time.
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      1. USMitch Wheat
    3. COI suggest that you keep this in a database table and get the COUNT on username which will be much more faster and easier.
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      1. USJames Jithin
 

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