如何在PHP中构建树？

Question

I have incoming POST array:

$parameters = array("1" , "2" , "3", "4", "5");
$parents = array("null" , "1" , "1", "3", "3");
$values = array("A" , "B" , "C", "D", "E");

The number of $parameters is unlimited.

So, I need to build a tree with nested parameters.

The resulting output should be:

1 -> {2 => value, 3 -> {4 => value, 5 => value}}

I tried to use the below loop:

foreach ($parameters["parameters"] as $index => $id) {
   if(!is_null($parameters["parents"][$index])){
      $output[$parameters["parents"][$index]][] = $id;
   }
}

But it works only for one tree level, I think I need to use a recursive approach.

Answer 1

You can use an iterative approach by keeping the references of the root elements in the array() $refs .
The code here misses the value for the elements which have children - it's your requirement - but you can keep it using explicit keys in the resulting array - say value => ..., children => array() for example.

$parameters = array('1', '2', '3', '4', '5');
$parents = array('null', '1', '1', '3', '3');
$values = array(    'A', 'B', 'C', 'D', 'E');

$tree = array();
$refs = array();
foreach ($parameters as $key=>$val) {
    if (isset($refs[$parents[$key]])) {
        if(!is_array($refs[$parents[$key]]))
            $refs[$parents[$key]] = array();
        $refs[$parents[$key]][$val] = $values[$key];
        $refs[$val] = &$refs[$parents[$key]][$val];
    } else {
        $tree[$val] = $values[$key];
        $refs[$val] = &$tree[$val];
    }
}

print_r($tree);

The above will print:

Array
(
    [1] => Array
        (
            [2] => B
            [3] => Array
                (
                    [4] => D
                    [5] => E
                )
        )
)