PHP – How to get all of possiblities sequence in an array / linked list

Basically I want to create a historical route in my app and I tried SplDoublyLinkedList, but I failed.

Now I decided to just use an array.

Suppose there is an array $array = [0,1,2,3]; . I want to generate all sequences with the following conditions.

$result = [
  [
    'sequence' => [0,1],
    'start' => 0,
    'finish' => 1,
    'via' => 'direct'
    'transit' => null
  ],

  [
    'sequence' => [0,1,2],
    'start' => 0,
    'finish' => 2,
    'via' => 'transit',
    'transit' => [1]
  ],
  [
    'sequence' => [0,1,2,3],
    'start' => 0,
    'finish' => 3,
    'via' => 'transit',
    'transit' => [1,2]
  ],
  [
    'sequence' => [1,2],
    'start' => 1,
    'finish' => 2,
    'via' => 'direct'
    'transit' => null
  ],
  [
    'sequence' => [1,2,3],
    'start' => 1,
    'finish' => 3,
    'via' => 'transit'
    'transit' => [2]
  ],
  [
    'sequence' => [2,3],
    'start' => 2,
    'finish' => 3,
    'via' => 'direct'
    'transit' => null
  ],

];

Answer

You can reach the desired result by using an outer and an inner loop:

$result = [];
$array = [0, 1, 2, 3];
$arrayCount = count($array);

for ($i = 0; $i < $arrayCount - 1; $i++) {

    for ($j = 0; $j < $arrayCount - $i - 1; $j++) {

        $arr = array_slice($array, $i, $j + 2);
        $count = count($arr);
        $direct = $count === 2;
        
        $result[] = [
            'sequence' => $arr,
            'start'    => $arr[0],
            'finish'   => $arr[$count - 1],
            'via'      => $direct ? 'direct' : 'transit',
            'transit'  => $direct ? null : array_slice($arr, 1, $count - 2)
        ];
    }
}

If you intend to generate many sequences and you must consider memory usage, then you can also use a generator:

function sequenceGenerator(array $array): iterator
{
    $arrayCount = count($array);
    
    for ($i = 0; $i < $arrayCount - 1; $i++) {

        for ($j = 0; $j < $arrayCount - $i - 1; $j++) {

            $arr = array_slice($array, $i, $j + 2);
            $count = count($arr);
            $direct = $count === 2;
            
            yield [
                'sequence' => $arr,
                'start'    => $arr[0],
                'finish'   => $arr[$count - 1],
                'via'      => $direct ? 'direct' : 'transit',
                'transit'  => $direct ? null : array_slice($arr, 1, $count - 2)
            ];
        }
    }
}

foreach (sequenceGenerator([0, 1, 2, 3]) as $sequence) {
    // Do something here, maybe store it to db?
    var_dump($sequence);
}