PHP: What is the complexity [i.e O(1),O(n)] of the function 'count'? [duplicate]

This question already has answers here: Is PHP's count() function O(1) or O(n) for arrays? 开发者_如何转开发 (3 answers) Closed 1 year ago.

What is the Big-O time complexity of the count() function for arrays?

Example

$x = array(1,2,3);
echo count($x); // how many operation does it takes to count the elements 
                // of the array? is it 3, or is it 1

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$ time php -r '$a=range(1,1000000); $b=0; for($i=0;$i<10;$i++) $b=count($a);'
real    0m0.458s
$ time php -r '$a=range(1,1000000); $a=array(1); $b=0; for($i=0;$i<10;$i++) $b=count($a);'
real    0m0.457s

Seems pretty O(1) to me.

Tested PHP version: PHP 5.3.3-1ubuntu9.1 with Suhosin-Patch (cli) (built: Oct 15 2010 14:00:18)

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Arrays have O(1) size- that is, their size is stored somewhere. The language updates the count on insertion/deletion.