题解 | #单词倒排#

给出三种解法，复杂程度依次递增

import java.util.LinkedList;
import java.util.Scanner;
import java.util.stream.Collectors;

public class Main {
    public static void main(String[] args) {
        try (Scanner in = new Scanner(System.in)) {
            String str = in.nextLine();
            // solution1(str);
            // solution2(str);
            solution3(str);
        }
    }

    private static void solution1(String str) {
        String[] words = str.split("\\W");
        for (int i = words.length - 1; i >= 0; i--) {
            System.out.print(words[i] + " ");
        }
    }

    private static void solution2(String str) {
        LinkedList<Character> stack = new LinkedList<>();
        for (char c : str.toCharArray()) {
            boolean isLetter = isLetter(c);
            if (isLetter) {
                stack.push(c);
            } else {
                if (!stack.isEmpty() && stack.peek() != ' ') {
                    stack.push(' ');
                }
            }
        }
        StringBuilder sb = new StringBuilder();
        LinkedList<Character> wordStack = new LinkedList<>();
        while (!stack.isEmpty()) {
            if (stack.peek() != ' ') {
                wordStack.push(stack.pop());
            } else {
                while (!wordStack.isEmpty()) {
                    sb.append(wordStack.pop());
                }
                sb.append(stack.pop());
            }
        }
        while (!wordStack.isEmpty()) {
            sb.append(wordStack.pop());
        }
        System.out.println(sb.toString().trim());
    }

    private static void solution3(String str) {
        StringBuilder sb = new StringBuilder();
        int len = str.length(), l = 0, r = 0, i = len - 1;
        while (i >= 0) {
            while (i >= 0) {
                if (isLetter(str.charAt(i))) {
                    r = i + 1;
                    break;
                }
                i--;
            }
            while (i >= 0) {
                if (!isLetter(str.charAt(i))) {
                    l = i + 1;
                    i--;
                    break;
                }
                if (isLetter(str.charAt(i)) && i == 0) {
                    l = 0;
                    i--;
                    break;
                }
                i--;
            }
            sb.append(str, l, r).append(" ");
        }
        System.out.println(sb);
    }

    private static boolean isLetter(char c) {
        return ('a' <= c && c <= 'z') || ('A' <= c && c <= 'Z');
    }
}