Recursive list of items in PHP, unknown depth and nodes - php

Question

gurus!
First of all, I've spent half a day googlin'n'stackoverflowing but couldn't find a solution. This is my first time working with recursions. Hope someone can help.
I have a MySQL table, this is kind of referal system:
Table 'users'
ID SPONSORID
---------
1 2
2 1
3 1
4 1
... ...
There are several things to keep in mind:
Users 1 and 2 are sponsors/referals of each other.
Each user can have unlimited number of referals.
Each user's referal becomes a sponsor as well and can also have unlimited number of referals
Depth is unlimited.
The task is to recursively build a tree of a single "team", like:
User 1
User 2
User 1
User 5
...
....
User 3
User 295
User 356
....
User 4
and so on...
Here's what I'm trying to do:
$team = Array();
function build_team( $userID, $team ){
if ( !in_array($userID, $team ) :
// get 1st level of referals
// returns associative array ('id', 'login', 'sponsorid')
$referals = get_user_referals( $userID );
for ( $i=0; $i<count($referals); $i++ ) :
$team[] = $referals[$i];
build_team( $referals[$i]['id'] );
endfor;
endif;
}
And also tried putting that IF inside the FOR block, but it still goes in infinite loop. As I understand I need a condition to quit recursion when there's no depth level but I can't understand how to calculate/determine it. Any suggestions?

Answer 1

Keep users ids, whom are already "built", somewhere. As you said yourself - "Users 1 and 2 are sponsors/referals of each other.", so there is your infinite loop.
Something like
if (!in_array($userId, $already_looped_users){
//continue loop...
}
Adding some code:
$team = Array();
function build_team( $userID, $team ){
if ( !in_array($userID, $team ) :
// get 1st level of referals
// returns associative array ('id', 'login', 'sponsorid')
$referals = get_user_referals( $userID );
if (count($referals) > 0){ //added this line
for ( $i=0; $i<count($referals); $i++ ) :
$team[] = $referals[$i];
$team[$referals[$i] = build_team( $referals[$i]['id'], $team ); // i've edited this line
endfor;
return $team;
}
endif;
}