字符串旋转问题 

public static void reverse(char[] chas, int start, int end) {
		char tmp = 0;
		while (start < end) {
			tmp = chas[start];
			chas[start] = chas[end];
			chas[end] = tmp;
			start++;
			end--;
		}
	}
	public static void rotate1(char[] chas, int size) {
		if (chas == null || size <= 0 || size >= chas.length) {
			return;
		}
		reverse(chas, 0, size - 1);
		reverse(chas, size, chas.length - 1);
		reverse(chas, 0, chas.length - 1);
	}
	public static void rotate2(char[] chas, int size) {
		if (chas == null || size <= 0 || size >= chas.length) {
			return;
		}
		int start = 0;
		int end = chas.length - 1;
		int lpart = size;
		int rpart = chas.length - size;
		int s = Math.min(lpart, rpart);
		int d = lpart - rpart;
		while (true) {
			exchange(chas, start, end, s);
			if (d == 0) {
				break;
			} else if (d > 0) {
				start += s;
				lpart = d;
			} else {
				end -= s;
				rpart = -d;
			}
			s = Math.min(lpart, rpart);
			d = lpart - rpart;
		}
	}
	public static void exchange(char[] chas, int start, int end, int size) {
		int i = end - size + 1;
		char tmp = 0;
		while (size-- != 0) {
			tmp = chas[start];
			chas[start] = chas[i];
			chas[i] = tmp;
			start++;
			i++;
		}
	}