Calculate the sum of suffixes similarities of a string

sum_of_suffixes_similarities_of_a_string.php

<?php

/**
 * Creates an input prompt with an optional title.
 *
 * @param string|null $title
 * @return string
 */
function input(string $title = null): ?string
{
    if ($title) {
        print($title);
    }

    return trim(fgets(STDIN, 1024));
}

/**
 * Outputs given string.
 *
 * @param string $str
 * @param bool $newLine
 */
function output(string $str, bool $newLine = false): void
{
    if ($newLine) $str .= PHP_EOL;

    print_r($str);
}

/**
 * Get character counts of similar prefixes of two strings.
 *
 * @param string $a
 * @param string $b
 * @return int
 */
function similarity(string $a, string $b): int {
    $i = 0;

    while ($i < strlen($a) && $i < strlen($b)) {
        if ($a[$i] === $b[$i])  $i++;
        else { break; }
    }

    return $i;
}

/**
 * Get sum of suffixes similarity counts of a string
 *
 * @param string $str
 * @return int
 */
function sumOfSuffixesSimilarity(string $str): int {
    // The similarity of string with itself is always up to be length of itself
    $sum = strlen($str);

    for ($i = 1; $i < strlen($str); $i++) {
        $sum += similarity($str, substr($str, $i));
    }

    return $sum;
}

function main()
{
    while (input('Type \'e\' to exit or press enter to continue.') !== 'e') {
        $count = (int)input('Please, enter count of test cases: ');
        $testCases = [];

        for ($i = 0; $i < $count; $i++) {
            $testCases[] = input();
        }

        if (!empty($testCases)) {
            output('Sum of suffixes similarity of the given test cases: ', true);

            foreach ($testCases as $testCase) {
                output(sumOfSuffixesSimilarity($testCase), true);
            }
        }
    }
}

main();

Execute php sum_of_suffixes_similarities_of_a_string.php command to run the CLI program.