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<?php <?php /** * ############################################################################ * Implementation of Mergesort algorithm in PHP * Tobias Baldauf, 20120624 */ /** * ############################################################################ * Let's define our data to work with */ $data = array(8,4,1,9,5,7,3,2,6,0); /** * ############################################################################ * The nitty gritty */ // This is it! Get the data to process, split it into halfs and compare // Returns: freshly sorted, reassembled array from split array-parts function mergesort($data) { // Only process if we're not down to one piece of data if(count($data)>1) { // Find out the middle of the current data set and split it there to obtain to halfs $data_middle = round(count($data)/2, 0, PHP_ROUND_HALF_DOWN); // and now for some recursive magic $data_part1 = mergesort(array_slice($data, 0, $data_middle)); $data_part2 = mergesort(array_slice($data, $data_middle, count($data))); // Setup counters so we can remember which piece of data in each half we're looking at $counter1 = $counter2 = 0; // iterate over all pieces of the currently processed array, compare size & reassemble for ($i=0; $i<count($data); $i++) { // if we're done processing one half, take the rest from the 2nd half if($counter1 == count($data_part1)) { $data[$i] = $data_part2[$counter2]; ++$counter2; // if we're done with the 2nd half as well or as long as pieces in the first half are still smaller than the 2nd half } elseif (($counter2 == count($data_part2)) or ($data_part1[$counter1] < $data_part2[$counter2])) { $data[$i] = $data_part1[$counter1]; ++$counter1; } else { $data[$i] = $data_part2[$counter2]; ++$counter2; } } } return $data; } // Initiate the recursive magic by calling the function once & print the output for our viewing pleasure $data = mergesort($data); print_r($data); ?>