《程序员代码面试指南》第五章 字符串问题 翻转字符串

题目

翻转字符串

java代码

package com.lizhouwei.chapter5;

/**
 * @Description: 翻转字符串
 * @Author: lizhouwei
 * @CreateDate: 2018/4/25 20:09
 * @Modify by:
 * @ModifyDate:
 */
public class Chapter5_11 {

    public String reverse(String str) {
        if (str == null) {
            return null;
        }
        char[] chars = str.toCharArray();
        reverse(chars, 0, chars.length - 1);
        int start = -1;
        int end = -1;
        for (int i = 0; i < chars.length; i++) {
            if (chars[i] != ' ') {
                start = i == 0 || chars[i - 1] == ' ' ? i : start;
                end = i == chars.length - 1 || chars[i + 1] == ' ' ? i : end;
            }
            if (start != -1 && end != -1) {
                reverse(chars, start, end);
                start = -1;
                end = -1;
            }
        }

        return String.valueOf(chars);
    }
    public String reverseByK(String str,int k) {
        if (str == null) {
            return null;
        }
        char[] chars = str.toCharArray();
        reverse(chars, 0,k-1);
        reverse(chars, k,chars.length - 1);
        reverse(chars, 0, chars.length - 1);
        return String.valueOf(chars);
    }
    public void reverse(char[] chars, int start, int end) {
        char temp = ' ';
        while (start < end) {
            temp = chars[start];
            chars[start++] = chars[end];
            chars[end--] = temp;
        }
    }

    //测试
    public static void main(String[] args) {
        Chapter5_11 chapter = new Chapter5_11();
        String str1 = "dog loves pig";
        String result1 = chapter.reverse(str1);
        System.out.println("dog loves pig 翻转：" + result1);
        String str2 = "1234567ABCD";
        String result2 = chapter.reverseByK(str2,7);
        System.out.println("1234567ABCD 左半区和右半区调整：" + result2);
     }
}

结果