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recursion_mystery15

Language/Type: PHP recursion recursion mystery

For each of the calls to the following recursive function below, indicate what value is returned: 

function recursion_mystery15($s) {
    if (strlen($s) == 0) {
        return $s;
    } elseif (strlen($s) % 2 == 0) {
        $rest = substr($s, 0, strlen($s) - 1);
        $last = $s[strlen($s) - 1];
        return $last . recursion_mystery15($rest);
    } else {
        $first = $s[0];
        $rest = substr($s, 1);
        return "($first)" . recursion_mystery15($rest);
    }
}
recursion_mystery15("hi");
recursion_mystery15("php");
recursion_mystery15("quirk");
recursion_mystery15("recursion");

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