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POPHP Arrays - Remove duplicates ( Time complexity )
 

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  1. POPHP Arrays - Remove duplicates ( Time complexity )
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    <p>Okay this is not a question of "how to get all uniques" or "How to remove duplicates from my array in php". This is a question about the time complexity.</p> <p>I figured that the <code>array_unique</code> is somewhat O(n^2 - n) and here's my implementation:</p> <pre><code>function array_unique2($array) { $to_return = array(); $current_index = 0; for ( $i = 0 ; $i &lt; count($array); $i++ ) { $current_is_unique = true; for ( $a = $i+1; $a &lt; count($array); $a++ ) { if ( $array[$i] == $array[$a] ) { $current_is_unique = false; break; } } if ( $current_is_unique ) { $to_return[$current_index] = $array[$i]; } } return $to_return; } </code></pre> <p>However when benchmarking this against the <code>array_unique</code> i got the following result:</p> <p>Testing (array_unique2)... Operation took 0.52146291732788 s. </p> <p>Testing (array_unique)... Operation took 0.28323101997375 s.</p> <p>Which makes the array_unique twice as fast, my question is, why ( Both had the same random data ) ?</p> <p>And a friend of mine wrote the following:</p> <pre><code>function array_unique2($a) { $n = array(); foreach ($a as $k=&gt;$v) if (!in_array($v,$n)) $n[$k]=$v; return $n; } </code></pre> <p>which is twice as fast as the built in one in php.</p> <p>I'd like to know, why?</p> <p>What is the time-complexity of array_unique and in_array?</p> <p><strong>Edit</strong> I removed the count($array) from both loops and just used a variable in the top of the function, that gained 2 seconds on 100 000 elements!</p>
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    1. COIs PHP really a good choice if your concern is efficient execution?
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      1. USChris Ballance
    2. COHaha, guess not, but that's not the point here. I generally don't use PHP. But i found this very interesting while playing around.
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    3. COYour first function isn’t correct: array_unique2(array(1, 2)) just returns array(2).
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