Tree-shaped algorithm _php

Test data
$ar = Array (
Array (id=>1,pid=>0),
Array (id=>2,pid=>0),
Array (id=>3,pid=>2),
Array (id=>4,pid=>0),
Array (id=>5,pid=>3),
Array (id=>6,pid=>1),
Array (id=>7,pid=>1),
Array (id=>8,pid=>6),
Array (id=>9,pid=>7),
Array (id=>10,pid=>9)
);

Sort function
function cmd ($a, $b) {
if ($a [pid]== $b [PID]) return 0;
return $a [pid]> $b [pid]?1:-1;
}

In order to avoid the presence of a parent node behind a child node in the data, which occurs after multiple modifications to the data
The purpose of sorting is to prevent the confusion caused by this situation
Uasort ($ar, CMD);

Defining the target array
$d = Array ();
Defines an indexed array that records the position of the node in the destination array
$ind = Array ();

foreach ($ar as $v) {
$v [Child] = array (); Attach a child item to each node
if ($v [pid] = = 0) {
$i = count ($d);
$d [$i] = $v;
$ind [$v [id]] =& $d [$i];
}else {
$i = count ($ind [$v [Pid]][child]);
$ind [$v [pid]][child][$i] = $v;
$ind [$v [id]] =& $ind [$v [pid]][child][$i];
}
}
Check Results
Print_r ($d);
?>

Algorithm features: Using the B + Tree concept, only one cycle can generate a tree array

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