MathPHP\Sequence\Advanced::lookAndSay PHP Метод

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lookAndSay() публичный статический Метод

1, 11, 21, 1211, 111221, 312211, 13112221, 1113213211, ... To generate a member of the sequence from the previous member, read off the digits of the previous member, counting the number of digits in groups of the same digit. 1 is read off as "one 1" or 11. 11 is read off as "two 1s" or 21. 21 is read off as "one 2, then one 1" or 1211. 1211 is read off as "one 1, one 2, then two 1s" or 111221. 111221 is read off as "three 1s, two 2s, then one 1" or 312211. https://en.wikipedia.org/wiki/Look-and-say_sequence https://oeis.org/A005150 Example: n = 6 Sequence: 1, 11, 21, 1211, 111221, 312211 Array index: 1, 2, 3, 4, 5, 6

public static lookAndSay ( integer $n ) : array
$n	integer	How many numbers in the sequence
Результат	array	of strings indexed from 1

    public static function lookAndSay(int $n) : array
    {
        if ($n <= 0) {
            return [];
        }
        // Initialize
        $list = [1 => '1'];
        $previous = '1';
        // Base case
        if ($n === 1) {
            return $list;
        }
        for ($i = 2; $i <= $n; $i++) {
            $sequence = "";
            $count = 1;
            $len = strlen($previous);
            for ($j = 1; $j < $len; $j++) {
                if (substr($previous, $j, 1) === substr($previous, $j - 1, 1)) {
                    $count++;
                } else {
                    $sequence .= $count . substr($previous, $j - 1, 1);
                    $count = 1;
                }
            }
            $sequence .= $count . substr($previous, $j - 1, 1);
            $previous = $sequence;
            $list[$i] = $sequence;
        }
        return $list;
    }

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