语言 API

import java.io.*;
import java.util.*;

public class Main {
    public static void main(String[] args) throws IOException {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        PrintWriter pw = new PrintWriter(System.out);

        String[] split = br.readLine().split(" ");
        for (int i = split.length - 1; i >= 0; i--) {
            pw.print(split[i]);
            if (i > 0) {
                pw.print(' ');
            }
        }
        pw.println();

        pw.flush();
        pw.close();
        br.close();
    }
}

手写

import java.io.*;
import java.util.*;

public class Main {
    public static void main(String[] args) throws IOException {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        PrintWriter pw = new PrintWriter(System.out);

        String str = br.readLine();
        StringBuilder builder = new StringBuilder();
        int left = str.length() - 1, right = str.length();
        while (left >= 0) {
            while (left >= 0 && str.charAt(left) != ' ') {
                left--;
            }
            pw.printf("%s ", str.substring(left + 1, right));
            right = left;
            left--;
        }
        pw.println();

        pw.flush();
        pw.close();
        br.close();
    }
}