leetcode-08-[151]翻转字符串里的单词[卡码网55]右旋转字符串

一、[151]翻转字符串里的单词

重点：见注释

class Solution {
    public String reverseWords(String s) {
        //1、移除多余的空格
        StringBuilder stringBuilder = removeSpace(s);
        //2、反转整个字符串
        reverse(stringBuilder,0,stringBuilder.length()-1);
        //3、反转每个单词
        reverseEachWord(stringBuilder);
        return stringBuilder.toString();
    }
    StringBuilder removeSpace(String s){
        StringBuilder stringBuilder=new StringBuilder();
        int left=0,right=s.length()-1;
        while(s.charAt(left)==' '){
            left++;
        }
        while(s.charAt(right)==' '){
            right--;
        }
        for(int i=left;i<right+1;i++){
            if(s.charAt(i)!=' '){
                stringBuilder.append(s.charAt(i));
            }else if(stringBuilder.charAt(stringBuilder.length()-1)!=' '){
                //若结束位置不为空格，则加个空格，否则什么也不做
                stringBuilder.append(s.charAt(i));
            }
        }
        return stringBuilder;
    }
    //设置开始结束的标记
    void reverse(StringBuilder stringBuilder,int left,int right){
        while(left<right){
            char tmp = stringBuilder.charAt(left);
            //设置值setCharAt
            stringBuilder.setCharAt(left,stringBuilder.charAt(right));
            stringBuilder.setCharAt(right,tmp);
            left++;
            right--;
        }
    }
    //注意一下
    void reverseEachWord(StringBuilder stringBuilder){
        int left=0,right=1;
        int n=stringBuilder.length();
        while(left<n){
            while(right<n&&stringBuilder.charAt(right)!=' '){
                right++;
            }
            reverse(stringBuilder,left,right-1);
            left=right+1;
            right=left+1;
        }
    }

}

二、[卡码网55]右旋转字符串

重点：技巧

反转三次

import java.util.Scanner;

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();
        char[] chars=s.toCharArray();
        reverse(chars,0,len-1);
        reverse(chars,0,n-1);
        reverse(chars,n,len-1);
        System.out.println(chars);
    }
    public static void reverse(char[] ch,int start,int end){
        while(start<end){
            char tmp=ch[start];
            ch[start]=ch[end];
            ch[end]=tmp;
            start++;
            end--;
        }
    }
}