php - Finding all possible ways to swap cards -

i working on php application finds possible ways swap cards. each user has @ least 1 card. when user request card, application shows him possible ways swap card in excange card requested.

lets that:

user 1 has card type user 2 has card type b  user 3 has card type c  

and lets assume that:

user 1 wants card type c user 2 wants card type user 3 wants card type b 

if user 1 requests card c, solution that:

user 1 gives user 2 card user 2 gives user 3 card user 3 gives user 1 card 

but if there 2 other users:

user 4 has card type b & wants card type user 5 has card type c & wants card type b 

now, if user 1 requests card c, there 1 other solution besides 1 above :

user 1 gives user 4 card user 4 gives user 5 card user 5 gives user 1 card 

there no limit in terms of how many cards user may have or request. far, created 2 sql tables. table "cards" keeps track of each userid , cardid. table "requests" keeps track of each userid , desired cardid.

i wouldn't use pure php this. rather create mysql table stores record each user, recording card user has card wants. then, run this:

$sql = "select * users"; $result = $this->db->query(); $users = $result->getall(); //a list of users.  foreach ($users $user) {    $sql = "select * users cardid = '$user->wantedcardid'";    $result = $this->db->query($sql);     if (! $result->has_rows())    {       echo "no other users $user->wantedcardid found.";       continue;    }     $cardholder = $result->row();    echo: "user $cardholder->id gives $user->id card"; } 

if using plain php, this:

//populate array containing list of users , cards.  $users = array();  $user[1] = new stdclass();; $user[1]->cardid = 2; $user[1]->wantedid = 3;  $user[2] = new stdclass(); $user[2]->cardid = 3; $user[2]->wantedid = 2; // .....  foreach ($users $userid=>$user) {    //run secondary loop through users find have card    //this user wants.    foreach ($users $holderid=>$cardholder)    {       if ($cardholder->cardid != $user->wantedid)          continue;       echo "user $holderid gives $userid card";    } }