归并排序

$input = array(6, 5, 3, 1, 8, 7, 2, 4);

function merge_sort($arr)

{

if (count($arr) <= 1) 

{

return $arr;

}

$left = array_slice($arr, 0, (int)(count($arr)/2));

$right = array_slice($arr, (int)(count($arr)/2));

$left = merge_sort($left);

$right = merge_sort($right);

$output = merge($left, $right);

return $output;

}

function merge($left, $right)

{

$result = array();

while (count($left) > 0 && count($right) > 0) 

{

    if ($left[0] <= $right[0]) 

    {

    array_push($result,

    array_shift($left));

    } 

    else 

    {

    array_push($result,

    array_shift($right));

    }

}

array_splice($result, count($result), 0, $left);

array_splice($result, count($result), 0, $right);

return $result;

}

// 1, 2, 3, 4, 5, 6, 7, 8

$output = merge_sort($input);

var_dump($output);