MaxCharacter.php

<?php

/**
 * This function returns the character which is repeated maximum number of
 * times in the given string.
 *
 * @param  string  $string
 * @return string
 * @throws \Exception
 */
function maxCharacter(string $string): string
{
    // Throw an exception if the string is empty.
    if (empty($string)) {
        throw new \Exception('Please pass a non-empty string value.');
    }

    // Initialize an associative array to hold character counts.
    $characterCountTable = [];

    // Convert the string to lowercase for case-insensitive analysis.
    $string = strtolower($string);

    // Convert the string into an array of characters.
    $characters = str_split($string);

    // Loop through the characters to populate the count table.
    foreach ($characters as $character) {
        // Initialize or update the count of the current character.
        $currentCharacterCount = isset($characterCountTable[$character]) ? $characterCountTable[$character] + 1 : 1;

        // Update the count in the table.
        $characterCountTable[$character] = $currentCharacterCount;
    }

    // Sort the count table in descending order.
    arsort($characterCountTable);

    // Return the character that appears most frequently.
    return array_keys($characterCountTable)[0];
}