Find array in array, in sequence

Question

How to code up a [find-array-in-array] function?

Psuedo-code

Haystack:

array(0=a, 1=b, 2=a, 3=b, 4=c,         


        

Answer 1

If the haystack consists of letters, you can do this in the string domain:

$haystack = array('a', 'b', 'a', 'b', 'c', 'c', 'a', 'b', 'd', 'c', 'a', 'b', 'a', 'b', 'c');
$haystack = join('', $haystack);

preg_match_all('/abc/', $haystack, $matches, PREG_OFFSET_CAPTURE);

print_r(array_map(function($item) {
  return range($item[1], $item[1] + strlen($item[0]) - 1);
}, $matches[0]));

Output:

Array
(
    [0] => Array
        (
            [0] => 2
            [1] => 3
            [2] => 4
        )

    [1] => Array
        (
            [0] => 12
            [1] => 13
            [2] => 14
        )

)

With potentially multiple characters inside the haystack, you need to resort to this:

$haystack = array('a', 'b', 'a', 'b', 'c', 'c', 'a', 'b', 'd', 'c', 'a', 'b', 'a', 'b', 'c');
$needle = array('a', 'b', 'c');

// cache array sizes
$haystack_len = count($haystack);
$needle_len = count($needle);

// shortlist the possible starting keys
$possible_keys = array_keys($haystack, $needle[0], true);

$results = array();

foreach ($possible_keys as $index) {
    // start searching
    $i = $index; $j = 0;
    while ($i < $haystack_len && $j < $needle_len) {
        if ($haystack[$i] !== $needle[$j]) {
            continue 2; // no match
        }
        ++$i; ++$j;
    }
    // match
    $results[] = range($index, $index + $needle_len - 1);
}

print_r($results);