replaceRepeats.php: Interview question of the week; https://buttondown.com/cassidoo/archive/the-beginning-is-the-word-and-the-end-is-silence/

replaceRepeats.php

/**
 *
 * Replaces sequences of repeated numeric characters in a string with the length of that sequence.
 *
 * @param $inputString string A string of numeric characters
 * @param $numberToReplaceWithLengthsOf int A single digit (0-9)
 *
 */
function replaceRepeats(string $inputString, int $numberToReplaceWithLengthsOf): string
{
    $length = strlen($inputString);
    $resultString = '';
    $bufferedCountOfRepeats = 0;

    for ($i = 0; $i < $length; $i++) {

        $currentChar = $inputString[$i];
        $currentChatAsInt = intval($currentChar);
        if ($currentChatAsInt === $numberToReplaceWithLengthsOf && $bufferedCountOfRepeats) {
            $bufferedCountOfRepeats++;
        } elseif ($currentChatAsInt === $numberToReplaceWithLengthsOf && !$bufferedCountOfRepeats) {
            $bufferedCountOfRepeats = 1;
        } elseif ($currentChatAsInt !== $numberToReplaceWithLengthsOf && $bufferedCountOfRepeats) {
            $resultString = $resultString . strval($bufferedCountOfRepeats);
            $bufferedCountOfRepeats = 0;
            $resultString = $resultString . $currentChar;
        } else {
            $resultString = $resultString . $currentChar;
        }
    }
    if ($bufferedCountOfRepeats) {
        $resultString = $resultString . strval($bufferedCountOfRepeats);
    }

    return $resultString;

}