Question

Not sure what I’m doing wrong with this recursion function.
I have an array with a tree of a website and a page I’m looking for can be infinitely deep.
The function goes through all possibilities but sometimes doesn’t stop when it finds the right “page”.

The array

$haystack = array(
    array("id" => 1,"parent" => 0,"route" => "home","children" => array()),
    array("id" => 2,"parent" => 0,"route" => "news","children" => array()),
    array("id" => 3,"parent" => 0,"route" => "photography","children" => array(
                array("id" => 6,"parent" => 3,"route" => "photography/portraits","children" => array()),
                array("id" => 7,"parent" => 3,"route" => "photography/countries","children" => array()),
                array("id" => 8,"parent" => 3,"route" => "photography/landscapes","children" => array(
                                array("id" => 9,"parent" => 8,"route" => "photography/landscapes/city","children" => array()),
                                array("id" => 10,"parent" => 8,"route" => "photography/landscapes/wilderness","children" => array())
                            )
                )
        )
    ),
    array("id" => 4,"parent" => 0,"route" => "about","children" => array()),
    array("id" => 5,"parent" => 0,"route" => "contact","children" => array()),
);

The recursion function

function recurse($needle = -1, $haystack = NULL){
    $_tmp = array();

    foreach($haystack as $key => $item)
    {
        echo $needle ." === ". $item["id"] . "<br/>";

        if((string)$item["id"] === (string)$needle){
            echo "Found: " . $needle . "<br/><br/>";
            $_tmp = $item;
            break;
            //return $item;   <-- this doesn't work either
        } else {
            $_tmp = recurse($needle, $item["children"]);
        }
    }
    return $_tmp;
}

Test cases:

$test = recurse(3);
print_r($test);

$test = recurse(7);
print_r($test);

$test = recurse(9);
print_r($test);

Last test outputs:

9 === 1
9 === 2
9 === 4
9 === 7
9 === 8
9 === 11
9 === 12
9 === 13
9 === 14
9 === 15
9 === 3
9 === 9
Found: 9  <-- should stop here, but continues

9 === 5
9 === 6
Array
(
)

Answer 1

Here is a slightly modified recurse function that fixes the problem you have:

 function recurse($needle = -1, $haystack = NULL){
    static $_tmp = array();

    if (count($_tmp) == 0 && $haystack != NULL && count($haystack) > 0) {
       foreach($haystack as $key => $item) {
          if (count($_tmp) == 0) {
              echo $needle ." === ". $item["id"] . "<br/>\n";

              if((string)$item["id"] === (string)$needle){
                  echo "Found: " . $needle . "<br/>\n";
                  $_tmp = $item;
                  break;
              } elseif (!empty($item["children"])) {
                  echo "calling ". $item["id"]. ".children <br/>\n";
                  $_tmp = recurse($needle, $item["children"]);
              }
          }
       }
    }
    return $_tmp;
}

Basically it declares a static variable $_tmp that gets initialized only once and and then a check to process the loop only if $_tmp is empty makes sure to stop further processing once needle has been found.

Online working demo of above code