Generate a random sequence of "pattern lock" numbers

Question

Today, my friend raised a challenge that I still can’t solve: "Create a random sequence of numbers in PHP"

The numbers are arranged as dial-pad / pattern-lock, which consist of 1-9 keys in 3 rows and 3 columns:

 ---------------------------
|                           |
|     1       2      3      |
|                           |
|     4       5      6      |
|                           |
|     7       8      9      |
|                           |
 ---------------------------

Now, given the length, we must create a random, non-repeating sequence of digits of the provided length, using the following criteria:

• The generated sequence should follow a certain direction / pattern passing only through adjacent numbers (possibly diagonally), for example (length: 8), 12569874:

   1 🡪 2
        🡫
   4    5 🡪 6
   🡩        🡫
   7 🡨 8 🡨 9 
  

• . . , 1 8, 6 4.

• , Android.

9: 12369874/5, 142536987 .., = 6: 987532 ..

rand():

  $chars = "123456789";
  $length = 9;
  $clen   = strlen( $chars )-1;
  $id  = '';

  for ($i = 0; $i < $length; $i++) {
      $id .= $chars[mt_rand(0,$clen)];
  }
  return ($id);

...

?

Answer 1

, . , :).

<pre>
<?php

// Keypad
$grid = [
    ['1', '2', '3'],
    ['4', '5', '6'],
    ['7', '8', '9'],
];

// Sequence Target Length
$target_length = 5;

// Place to store the Keypad sequence
$points = [];

// Starting Point
$x = rand(0, 2);
$y = rand(0, 2);

// Run through the process until we have the sequence at the desired length
while (count($points) < $target_length):

    // Check if the grid keypad entry has been used
    if ($grid[$x][$y]):
        // Hasn't been used, so stire it
        $points[] = $grid[$x][$y]; 
        // Mark it used 
        $grid[$x][$y] = NULL;
    endif;

    // Sanity Check, imagine if you will,.... target length of 9, and you hit 6 5 2 1,  You'll vault off into the twilight zone without this
    if ((!$grid[$x + 1][$y]) && (!$grid[$x][$y + 1]) && (!$grid[$x - 1][$y]) && (!$grid[$x][$y - 1])):
        // We have no where to go
        break;
    endif;

    // Start looking for possible values 
    do {
        $test_x = $x;
        $test_y = $y;
        $dir = rand(0, 3);

        switch ($dir):
            case (0):
                $test_y--; // Up
                break;
            case (1):
                $test_x++; // Right
                break;
            case (2):
                $test_y++; // Down
                break;
            case (3):
                $test_x--; // Left
                break;
        endswitch;
        // Optional Gibberish 
        echo "Moving from {$x}, {$y} to {$test_x}, {$test_y} --> " . (($grid[$test_x][$test_y] === NULL) ? 'FAILED' : 'OK!') . '<br>';

        // Keep going until we find a valid direction
    } while ($grid[$test_x][$test_y] === NULL);

    // assign the new coords
    $x = $test_x;
    $y = $test_y;

    // repeat
endwhile;

// report
echo implode('-', $points) . "\n";

?>
</pre>

Answer 2

, :

• , ,

, . , "", , . , .

, 1 9:

function randomSequence($len) {
    if ($len < 1 || $len > 9) return []; // No results
    $row = [null, 1, 1, 1, 2, 2, 2, 3, 3, 3];
    $col = [null, 1, 2, 3, 1, 2, 3, 1, 2, 3];
    $neighbors = [[], [2, 4, 5],       [1, 4, 5, 6, 3],          [2, 5, 6],
                      [1, 2, 5, 7, 8], [1, 2, 3, 4, 6, 7, 8, 9], [2, 3, 5, 8, 9],
                      [4, 5, 8],       [4, 5, 6, 7, 9],          [5, 6, 8]];
    // Shuffle the neighbor lists to implement the randomness:
    foreach ($neighbors as &$nodes) shuffle($nodes);

    $recurse = function ($seq) use (&$len, &$row, &$col, &$neighbors, &$recurse) {
        if (count($seq) >= $len) return $seq; // found solution
        $last = end($seq);
        echo "try " . json_encode(array_keys($seq)) . "\n";
        foreach ($neighbors[$last] as $next) {
            if (isset($seq[$next])) continue; // Skip if digit already used
            $result = $recurse($seq + [$next => $next]);
            if (is_array($result)) return $result;
        }
    };
    $choice = rand(1, 9);
    return array_keys($recurse([$choice => $choice]));
}

echo "result: " . json_encode(randomSequence(9)) . "\n";

, repl.it

Answer 3

, :

1 2
3 4

# Get which other numbers are "legal moves" from each number.
adjacency = {
    1: [2, 3],
    2: [1, 4],
    3: [1, 4],
    4: [2, 3]
}

# Get the length of code required.
n = 8
# Start at a random position;
pos = rand(keys(adjacency))
result = []
while (n > 0)
    n -= 1
    newpos = rand(adjacency[pos])
    result[] = newpos
    pos = newpos
print(result.join(', '))

, adjaceny, hardcoding.