字符串reverse

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package com.myway.study;

/**
 * 编程珠玑的题目：
 * 举例：比如abcdef 左移三位,则变成defabc
 * 

 * 条件限制：空间限制：可用内存为几十字节
 * 

 * 时间限制：花费时间与n成比例
 * User: zhangyong
 * Date: 14-5-27
 * Time: 下午8:24
 * To change this template use File | Settings | File Templates.
 */
public class Reverse {

    public static char[] reverse(char[] arr, int start, int end) {
        int n = arr.length;
        // abc  奇数
        // abcd 偶数
        int mid = (start + end) / 2;
        for (int i = start, j = end; i <= mid; i++, j--) {
            char temp = arr[i];
            arr[i] = arr[j];
            arr[j] = temp;
        }
        return arr;
    }

    public static char[] leftRotateString(char[] arr, int k) {
        //字符串abcdefgh -> defghabc
//      需要三步：
//      reverse(0,i-1); //cba defgh
//      reverse(i,n-1); //cba hgfed
//      reverse(0,n-1); //defghabc

        int n = arr.length;
        reverse(arr, 0, k - 1);
        reverse(arr, k, n - 1);
        reverse(arr, 0, n - 1);
        return arr;
    }

    public static void main(String[] args) {
        char[] arr = "abcdefg".toCharArray();
        leftRotateString(arr, 3);
        System.out.println(arr);
    }

}