Question 41378 in PHP Question posted in
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which algorithm php to create a secret Santa program

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]);
        }
    }
}

enter image description here

How can I take into account this blacklist please?

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2

Answers


  1. Chosen as BEST ANSWER
    0 
            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


  2. 0

    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 %sn", $people[$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 $pair ) {
    printf("%sn", json_encode($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.

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