Re-run function if false - php

Question

I'm working on code that takes a random value, checks if it's correct with a few checks and if it is, it'll return it. If it isn't, it's supposed to rerun the function untill one that does is found.
If the random value is correct it'll set a var to 1 like this: $chosen = 1; and then using a while loop it'll keep running the current function untill it's 0:
public function generate_chair($id, $optredenID)
{
$model = new Model_Shop;
// Get all the chairs for the given room
$chairs = $model->check_chair($id);
// Get an array of reserved chairs for a given event
$reserved = $model->get_reserved($optredenID);
do {
// If chosen = 0, all chairs are available.
// If chosen = 1, one of the chairs is not available
$chosen = 0;
// Create a new empty array
$rand_chairs = array();
// Pick a random chair
$chair = array_rand($chairs);
// Based off the amount chosen in the dorpdown, build array
switch($_POST['AantalPlaatsen']) {
case '1':
array_push($rand_chairs, $chair);
break;
case '2':
array_push($rand_chairs, $chair);
array_push($rand_chairs, $chair+1);
// Check if the chair chosen is the last chair in a row
// If it is, check for another chair
if($chair == 20 || $chair == 40 || $chair == 60 || $chair == 80 || $chair == 100 || $chair == 120 || $chair == 140 ||$chair == 160 ||
$chair == 180 || $chair == 200) {
$chosen = 1;
}
break;
case '3':
array_push($rand_chairs, $chair);
array_push($rand_chairs, $chair+1);
array_push($rand_chairs, $chair+2);
break;
case '4':
array_push($rand_chairs, $chair);
array_push($rand_chairs, $chair+1);
array_push($rand_chairs, $chair+2);
array_push($rand_chairs, $chair+3);
break;
}
// Check if one of the random generated chairs is in the reserved array
// If so, the chair is unavailable and new random must be generated
if( count(array_intersect( $rand_chairs, $reserved )) != 0 ) {
$chosen = 1;
}
} while ($chosen == 1);
return $rand_chairs;
What I wanted works now, but I'm wondering if anyone has a idea for another issue.
As shown in the switch-case, when the customer chooses 2 chairs and the first one is at the end of a row, it has to check for a new chair, because you can't spread multiple chairs over multiple rows.
The way I do this is with alot (too many) if statements. Does anyone know a better solution?

Answer 1

Why are you using recursion here? Why not just repeat the part of the function which you need to rerun?
do {
$chosen = 0;
// create a new empty array
$rand_chairs = array();
// Pick a random chair
$chair = array_rand($chairs);
...
foreach($rand_chairs as $key) {
if(in_array($key, $reserved)) {
$chosen = 1;
break; // oops, we need to rerun
}
}
} while( $chosen == 1 )
This uses a do-while control structure, which runs through the body at least once.
The break statement exits out of the while loop early, since the key has been found.
Additionally, instead of the foreach statement, you could use array_intersect():
if( count(array_intersect( $rand_chairs, $reserved )) != 0 ) {
$chosen = 1;
}

Answer 2

Faster algorithm would go something like this: you would run it one row of seats at a time, since "sitting at opposite ends of adjacent rows" isn't really "sitting together"...
Boolean seatsTaken()
int startsAt(), runLength()
For each row in seatsTaken
adjacent = 0
seat = 0
while not row(seat):
++adjacent
if adjacent > 0:
startsAt.push(seat-adjacent)
runLength.push(adjacent)
When this is done you have an array of all the blocks. Select only the blocks that are big enough (runLength() >= needed) and randomly choose one of them