一、151.翻转字符串里的单词

题目链接：https://leetcode.cn/problems/reverse-words-in-a-string/
文章讲解：https://programmercarl.com/0151.%E7%BF%BB%E8%BD%AC%E5%AD%97%E7%AC%A6%E4%B8%B2%E9%87%8C%E7%9A%84%E5%8D%95%E8%AF%8D.html#%E7%AE%97%E6%B3%95%E5%85%AC%E5%BC%80%E8%AF%BE
视频讲解：https://www.bilibili.com/video/BV1uT41177fX

1.1 初见思路

1.先翻转每个单词，再翻转整个字符串
2.消除多余空格

1.2 具体实现

class Solution {
    public String reverseWords(String s) {
 //1.把字符串去掉多余空格
        StringBuilder stringBuilder = removeMoreSpace(s);
       
        //2.翻转整个字符串
        reverseWholeStr(stringBuilder);
        //3.翻转每个单词
        reverAllWord(stringBuilder);
        return stringBuilder.toString();
    }

    public  StringBuilder removeMoreSpace(String s){
        StringBuilder stringBuilder = new StringBuilder();
        int left =0;
        int right = s.length()-1;
        while(s.charAt(left)==' '){
            left++;
        }
        while(s.charAt(right)==' '){
            right--;
        }
        for(int i=left;i<=right;i++){
            //如果是空格，则跳过,得保留一个空格的
            if(s.charAt(i)==' '){
                if(s.charAt(i-1)!=' '){
                    stringBuilder.append(' ');
                }
                continue;
            }
           // System.out.println("i="+i+"::::对应的s"+s.charAt(i));
            stringBuilder.append(s.charAt(i));
        }
        return stringBuilder;
    }

    public  void reversePartStr(StringBuilder sb,int left ,int right){
        while(left<right){
            char temp = sb.charAt(right);
            sb.setCharAt(right,sb.charAt(left));
            sb.setCharAt(left,temp);
            left++;
            right--;
        }
        
    }
    public  void reverseWholeStr(StringBuilder stringBuilder){
        reversePartStr(stringBuilder, 0, stringBuilder.length() - 1);
        System.out.println(stringBuilder);
    }

    public  void  reverAllWord(StringBuilder sb){
        int start = 0;
        int end = 1;
        int n = sb.length();
        while (start < n) {
            while (end < n && sb.charAt(end) != ' ') {
                end++;
            }
            reversePartStr(sb, start, end - 1);
            start = end + 1;
            end = start + 1;
        }
    }
}

1.3 重难点

二、 右旋字符串

题目链接：https://kamacoder.com/problempage.php?pid=1065
文章讲解：https://programmercarl.com/kamacoder/0055.%E5%8F%B3%E6%97%8B%E5%AD%97%E7%AC%A6%E4%B8%B2.html#%E5%85%B6%E4%BB%96%E8%AF%AD%E8%A8%80%E7%89%88%E6%9C%AC
视频讲解：https://www.bilibili.com/video/BV12A4y1Z7LP

2.1 初见思路

1.翻转整个字符串
2.反转前一段字符串
3.反转后一段字符串

2.2 具体实现

public class Main {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        int n = Integer.parseInt(in.nextLine());
        String s = in.nextLine();

        int len = s.length();  //获取字符串长度
        char[] chars = s.toCharArray();
        reverseString(chars, 0, len - 1);  //反转整个字符串
        reverseString(chars, 0, n - 1);  //反转前一段字符串，此时的字符串首尾尾是0,n - 1
        reverseString(chars, n, len - 1);  //反转后一段字符串，此时的字符串首尾尾是n,len - 1
        
        System.out.println(chars);

    }

    public static void reverseString(char[] ch, int start, int end) {
        //异或法反转字符串，参照题目 344.反转字符串的解释
        while (start < end) {
            ch[start] ^= ch[end];
            ch[end] ^= ch[start];
            ch[start] ^= ch[end];
            start++;
            end--;
        }
    }
}

2.3 重难点