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setCharAtstringBuilder.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--;}}
}