字符串翻转

1.编写程序，在原字符串中把字符串尾部的m个字符移动到字符串的头部，要求：长度为n的字符串操作时间复杂度为O(n)，空间复杂度为O(1)。 例如，原字符串为”Ilovebaofeng”，m=7，输出结果为：”baofengIlove”。

2、单词翻转。输入一个英文句子，翻转句子中单词的顺序，但单词内字符的顺序不变，句子中单词以空格符隔开。为简单起见，标点符号和普通字母一样处理。例如，输入“I am a student.”，则输出“student. a am I”。

代码实现：

package alg;



/**

 * @author zha

 *  字符串反转

 */

public class Alg1StringReserv {

    

    public static void main(String[] args) {

        String test = "ilovebaofeng";

        int index = 7 ;

        String re = reserve(test,index);

        System.out.println(re);

        

        String test2 = "I am a student.";

        char index2 = ' ';

        String re2 = reserve(test2,index2);

        System.out.println(re2);



    }

    

    //根据某一个特定的字符进行翻转

    private static String reserve(String test, char index) {

        

        char[] chars = test.toCharArray();

        int from = 0,to = 0;

        for (int i = 0; i < chars.length; i++) {

            char temp = chars[i];

            if(temp == index){

                to = i-1;

                turnOver(chars,from,to);

                from = i+1;

            }

        }

        

        if(to < chars.length - 1){

            turnOver(chars, from, chars.length-1);

        }

        

        turnOver(chars,0,chars.length-1);

        return new String(chars);

    }



    private static String reserve(String test, int index) {

        int length = test.length();

        int begine = （length - index - 1）%length;

        char[] chars = test.toCharArray();

        turnOver(chars,0,begine);

        turnOver(chars,begine+1,length-1);

        turnOver(chars,0,length-1);

        return new String(chars);

    }



    private static void turnOver(char[] chars, int begine, int to) {

        if(begine < to){

            for (; begine < to; begine++,to--) {

                swap(chars,begine,to);

            }

        }

        

    }



    private static void swap(char[] chars, int begine, int to) {

        char temp = chars[begine];

        chars[begine] = chars[to];

        chars[to] = temp;

        

    }



}

欢҉迎҉指҉出҉代҉码҉中҉不҉足҉的҉地҉方҉。