题解 | #单词倒排#

双指针 leetcode也有类似：https://leetcode-cn.com/problems/reverse-words-in-a-string/

import java.util.*;
public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        String s = sc.nextLine();
        char[] c = s.toCharArray();
        for (int i = 0; i < c.length; i++) {
            if (!Character.isLetter(c[i])) {
                c[i] = ' ';
            }
        }
        // 双指针法
        int left = 0;
        int right = c.length - 1;
        StringBuilder str = new StringBuilder();
        // 下面两行主要为了去除字符串前后的空格
        while (c[left] == ' ') left++;
        while (c[right] == ' ') right--;
      
        while (left <= right) {
            int index = right;
            while (index >= left && c[index] != ' ' ) index--;
            for (int i = index + 1 ; i <= right ; i++ ) str.append( c[i] );
            // 这一句可以使字符串最后没有空格，方便直接返回
            if (index > left) str.append(' ');
            while ( index >= left && c[index] == ' ' ) index--;
            right = index;
        }
        System.out.println(str.toString());
    }
}