Paginate Tree Array

Question

I am looking at trying to build pagination method for an array. I have an array something like below. Before you suggest making the pagination work for sql query, I have already done so and it did work for a flat array but a requirement is having this multidimensional tree array.

array = (
   item_id = 5,
   parent_id = 0,
   children = array(
      array(
         item_id = 20,
         parent_id = 5,
         children = array(
            array(
               item_id = 24,
               parent_id = 20
            ),
            array(
               item_id = 24,
               parent_id = 20
            )
         )
      )
   )
);

What methods that I can find don't seem to work with such an array since array_slice will only work on the first level of the array and doesn't take into consideration the children levels.

Answer 1

/*
$root = 
[
    'id' => 1,
    'children' => [...]
]

$queue[] = $root
$visiteds[] = $root
while ($queue){
    $current = array_shift($queue);
    // do whatever with the current ex: echo $current."<br>"
    if $current has children {
        foreach child {             
            if ($child NOT in $visiteds) { // $child not visited before
                $visiteds[] = $child // mark as visited                 
                $queue[] = $child // add to queue
                // do whatever with the child ex: echo $child ."<br>"
            }
        }
    }
}
*/

Note: if you want to visit exactly same children as required (for example 2 exactly same child must be visited twice then, remove $visiteds related parts. In this case be careful that your graph structure must not have cycling.)

You may consider to read about Graph Theory, Breadth First Search algorithm, Depth First Search algorithm.