How can PHP be used to find duplicate characters in a string?

To find duplicate characters in a string using PHP, we can iterate through each character in the string and keep track of how many times each character appears. If a character appears more than once, we can consider it a duplicate. We can store the duplicate characters in an array and return them at the end. 

function findDuplicateCharacters($str) {
    $charCount = [];
    $duplicates = [];

    for ($i = 0; $i < strlen($str); $i++) {
        $char = $str[$i];
        if (isset($charCount[$char])) {
            $charCount[$char]++;
        } else {
            $charCount[$char] = 1;
        }

        if ($charCount[$char] > 1 && !in_array($char, $duplicates)) {
            $duplicates[] = $char;
        }
    }

    return $duplicates;
}

$string = "hello";
$duplicates = findDuplicateCharacters($string);
print_r($duplicates);

Keywords

PHP string duplicate characters array_count_values foreach

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