Rotate String

public class Solution {
    /**
     * @param str: an array of char
     * @param offset: an integer
     * @return: nothing
     */
    public static char[] rotateString(char[] str, int offset) {
        if (str == null || str.length == 0){
            return str;
        }
        int len = str.length;
        offset %= len;
        reverse(str, 0, len - offset - 1);
        reverse(str, len - offset, len - 1);
        reverse(str, 0, len - 1);
        return str;
    }
    public static void reverse(char[] str, int start, int end){
        while (start < end){
            char temp = str[start];
            str[start] = str[end];
            str[end] = temp;
            start++;
            end--;
        }
    }
}