vector rotation problem

编程珠玑上的一道题目：将一个具有n个元素的一位向量向左旋转i个位置，

例如n=8，i=3，字符串“abcdefgh”转换为“defghabc”

思路一：考虑空间复杂度的情况下，利用临时变量t分别存放a、b、c，每次将剩下的defgh向前移动1位，再把abc依次放在字符串最后

思路二：书中给出了更好的方法，先把字符串abc看作a，把defgh看作b，所以原字符串为ab，翻转后为ba，步骤如下：

java实现：

/**
 * Created by hogarth on 2016/5/3.
 * A problem from programming pearls
 * Rotate String "abcdfefgh" to "defghabc"
 * Solution: AB->ArB->ArBr->(ArBr)r->BA
 */
import java.util.*;

public class vector_rotation {
    public static void main(String[] args) {
        Partition p = new Partition();
        String s = "abcdefgh";
        System.out.println("before:"+ s + " after:" + p.rotate(s,3));
    }

    public static class Partition {
        public String rotate(String s, int i) {
            char[] c = s.toCharArray();
            int length = c.length;
            reverse(c, 0, i-1);
            reverse(c, i, length-1);
            reverse(c, 0, length-1);

            return String.valueOf(c);
        }

        public void reverse(char[] c, int first, int last){
            for (int j = 0; j < len/2; j++){
                char tmp = c[first+j];
                c[first+j] = c[last-j];
                c[last-j] = tmp;
            }
        }
    }
}

输出：before:abcdefgh after:defhgabc