8. 旋转字符串

给定一个字符串和一个偏移量，根据偏移量旋转字符串(从左向右旋转)

样例

对于字符串 "abcdefg".

offset=0 => "abcdefg"
offset=1 => "gabcdef"
offset=2 => "fgabcde"
offset=3 => "efgabcd"

public class Solution {
    /**
     * @param str: An array of char
     * @param offset: An integer
     * @return: nothing
     */
    public void rotateString(char[] str, int offset) {
        // write your code here
        if (str == null || str.length == 0) {
			return;
		}
		offset = offset % str.length;
		reverse(str, 0, str.length - offset - 1);
		reverse(str, str.length - offset, str.length - 1);
		reverse(str, 0, str.length - 1);
	}
	
	private static void reverse(char[] str, int start, int end) {
		for (int i = start, j = end; i < j; i++, j--) {
			char temp = str[i];
			str[i] = str[j];
			str[j] = temp;
		}
    }
}