Write a function that takes a string as input and returns the string reversed.

Example:
Given s = "hello", return "olleh".

    public static String reverseString(String s) {if (s == null) {return null;}if (s.length() == 0) {return "";}int length = s.length();char[] chars = s.toCharArray();String result = "";for (int i = chars.length - 1; i >=0; --i) {result += chars[i];}return result;}

    public String reverseString(String s) {return new StringBuffer(s).reverse().toString();}