which algorithm php to create a secret Santa program - php

Question

I'm trying to make a draw for a secret Santa.
I collect in a table the information of the person and the name of the person on whom it should not fall (to avoid couples).
However during my PHP loop I can't take into account my exclusions
foreach ($supplier as $sup){
$exclude = $sup['blacklist'];
$data = $recipient;
$temp = array_diff($data[], array($exclude));
echo $temp[rand(0, sizeOf($temp))];
foreach ($recipient as $key=>$recip){
if ($sup['surname'] !== $recip['surname']){
$result[] = ['recipient' => $recip, 'supplier' => $sup];
unset($recipient[$key]);
}
}
}
How can I take into account this blacklist please?

Answer 1

shuffle($supplier);
shuffle($recipient);
// dump($supplier, $recipient);
$result = [];
foreach ($supplier as $sup){
$assign = false;
dump($sup);
foreach ($recipient as $key=>$recip){
dump($recip['surname']);
if ($sup['surname'] !== $recip['surname'] && $sup['blacklist'] !== $recip['surname'] && $sup['surname'] !== $recip['blacklist']){
$result[] = ['recipient' => $recip, 'supplier' => $sup];
dump($sup['surname']);
unset($recipient[$key]);
$assign = true;
}
if ($assign === true){
break;
}
}
}
return $result;
}
this is my code with shuffle

Answer 2

Your solution is fine, but with that nested loop it's going to start behaving poorly as the list of participants grows. You can accomplish the task with a single array and two linear passes over it:
$people = [
[ 'name' => 'alice', 'blacklist' => ['bob'] ],
[ 'name' => 'bob', 'blacklist' => ['alice'] ],
[ 'name' => 'carl', 'blacklist' => ['david'] ],
[ 'name' => 'david', 'blacklist' => ['carl'] ],
[ 'name' => 'elise', 'blacklist' => ['frank'] ],
[ 'name' => 'frank', 'blacklist' => ['elise'] ],
[ 'name' => 'georg', 'blacklist' => ['herb'] ],
[ 'name' => 'herb', 'blacklist' => ['george'] ]
];
function wrap_index($count, $index) {
$cur = $index;
if( $index == 0 ) {
$prev = $count - 1;
$next = $index + 1;
} else if( $index == $count - 1) {
$prev = $index - 1;
$next = 0;
} else {
$prev = $index - 1;
$next = $index + 1;
}
return [$prev, $cur, $next];
}
function array_swap(&$array, $a, $b) {
$tmp = $array[$a];
$array[$a] = $array[$b];
$array[$b] = $tmp;
}
function santify($people) {
shuffle($people);
$count = count($people);
for( $i=0; $i<$count; ++$i ) {
list($prev, $cur, $next) = wrap_index($count, $i);
if( in_array($people[$cur]['name'], $people[$next]['blacklist']) ) {
printf("%s in blacklist for %s\n", $people[$cur]['name'], $people[$next]['name']);
array_swap($people, $cur, $prev);
}
}
$pairs = [];
for( $i=0; $i<$count; ++$i ) {
list($prev, $cur, $next) = wrap_index($count, $i);
$pairs[] = [ $people[$cur]['name'], $people[$next]['name'] ];
}
return $pairs;
}
foreach( santify($people) as $pair ) {
printf("%s\n", json_encode($pair));
}
Output:
david in blacklist for carl
elise in blacklist for frank
["david","georg"]
["georg","carl"]
["carl","bob"]
["bob","herb"]
["herb","elise"]
["elise","alice"]
["alice","frank"]
["frank","david"]
There is a caveat to this approach, though. It will only work with strict 1:1 blacklist arrangements. Once there is a love triangle [or quardrangle or above] or any polyamory, neither of our solutions is equipped for these extra dimensions.