lc151翻转字符串里的单词

思路

后序截取单词，顺序添加到结果字符串中

代码

class Solution {
    public String reverseWords(String s) {
        s = s.trim();
        int j = s.length()-1, i = j;
        StringBuilder res = new StringBuilder();
        while (i >= 0){
            while (i >= 0 && s.charAt(i) != ' '){ i--; }
            res.append(s.substring(i+1,j+1) + " ");
            while (i >= 0 && s.charAt(i) == ' '){ i--; }
            j=i;
        }
        return res.toString().trim();
    }
}

卡码网55右旋转字符串

思路

先翻转整个字符串，再局部分别翻转，记得画图哦

代码

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();  //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--;
        }
    }
}