LookNSay-Iteration1.php

<?php

$input = 10;
$last = "1";

for ($i = 0; $i < $input; $i++) {
    echo $last . PHP_EOL;
    $last = lookNSay($last);
}

function lookNSay($last)
{
    $row = "";
    $cur = $last[0];

    $count = 1;
    for ($i = 1; $i <= strlen($last); $i++) {
        if ($i == strlen($last) || $cur != $last[$i]) {
            $row .= $count . $cur;
            $cur = $last[$i] ?? $last[$i-1];
            $count = 1;
        } else {
            $count++;
        }
    }
    
    return $row;
}


/**

1 
11
21
1211
111221
312211
13112221
1113213211
31131211131221
13211311123113112211

*/

LookNSay.php

<?php

$input = 10;


$result[0] = "1";

echo $result[0] . PHP_EOL;

for ($i = 1; $i < $input; $i++) {
    $result[$i] = lookNSay($result[$i-1], $i);
    echo $result[$i] . PHP_EOL;
}

function lookNSay($last, $c)
{
    $row = "";
    $cur = $last[0];
        
    $count = 1;
    for ($i = 1; $i <= strlen($last); $i++) {
        if ($i == strlen($last) || $cur != $last[$i]) {
            $row .= $count . $cur;
            $cur = $last[$i] ?? $last[$i-1];
            $count = 1;
        } else {
            $count++;
        }
    }
    
    return $row;
}


/**

1 
11
21
1211
111221
312211
13112221
1113213211
31131211131221
13211311123113112211

*/