php - How can I convert a series of parent-child relationships into an array of there sequence? -

i have bunch of parent child id in array given bellow,

 child => parent   array (   [1] => 0   ===>parent   [2] => 1   [4] => 1   [5] => 4   [6] => 2   [7] => 0   ===>parent   [8] => 2   [9] => 7   [10] => 2   [11] => 2   [12] => 2   [17] => 12   [18] => 17   [19] => 0    ===>parent   [20] => 19   [21] => 20   [22] => 20   [23] => 20 ) 

and parsing tree is

                 0->parent      ____________|___________________________     |                   |                   |     1(0's child)        7                   19->0 parent's child[1]->[0],[7]->0,[19]->0   __|_______            |                   |   |         |           9                   20   2         4 (2 & 4 1 parent's child)   |   |         |                            21,22,23   |         5   |  6,8,10,11,12             |             17             |             18 

and want take 0 root element id , check child , grand child, , result array like,

   $result = array         (         [0] => 1        -->i use categoryname here $myarray[1]['categoryname']         [1] => 1->2      ---> $myarray[1]['categoryname']->$myarray[2]['categoryname']         [2] => 1->2->6   --->and on         [3] => 1->2->8         [4] => 1->2->10         [5] => 1->2->11         [6] => 1->2->12         [7] => 1->2->12->17         [8] => 1->2->12->17->18         [9] => 1->4         [10] => 1->4->5         [11] => 7         [12] => 7->9         [13] => 19         [14] => 19->20         [15] => 19->20->21         [16] => 19->20->22         [17] => 19->20->23        ) 

similar convert series of parent-child relationships hierarchical tree? question, code is,

  $tree = $this->to_tree($array); function to_tree($array) { $flat = array(); $tree = array(); $abc = array();   foreach ($array $child => $parent)    {        if (!isset($flat[$child])) {         $flat[$child] = array();        }        if (!empty($parent)) {         $flat[$parent][$child] =& $flat[$child];        } else {          $tree[$child] =& $flat[$child];        }   }        return $tree; } 

and print hierarchical tree please me, thank you.