[LeetCode / Medium] 151. Reverse Words in a String (Java)

💬 Info

• 난이도 : Medium
• 문제 링크 : https://leetcode.com/classic/problems/reverse-words-in-a-string/description/
• 풀이 링크 : LeetCode/Medium/Reverse Words in a String.java

Problem

Given an input string s, reverse the order of the words.

A word is defined as a sequence of non-space characters. The words in s will be separated by at least one space.

Return a string of the words in reverse order concatenated by a single space.

Note that s may contain leading or trailing spaces or multiple spaces between two words. The returned string should only have a single space separating the words. Do not include any extra spaces.

Example

예시 1

• Input: s = "the sky is blue"
• Output: "blue is sky the"

예시 2

• Input: s = " hello world "
• Output: "world hello"
• Explanation: Your reversed string should not contain leading or trailing spaces.

예시 3

• Input: s = "a good example"
• Output: "example good a"
• Explanation: You need to reduce multiple spaces between two words to a single space in the reversed string.

Constraints

• 1 <= s.length <= $10^4$
• s contains English letters (upper-case and lower-case), digits, and spaces ' '.
  There is at least one word in s.

문제 이해

• 단어 뒤집기: 영단어로만 이뤄진 단어를 출력해야하는 데에 유의점이 있음!

알고리즘

풀이 시간 : 24분

• 공백 제거, 단어 분리
  • trim(), split() 사용
  • \\s+
    • \\s : 공백 문자
    • + : 하나 이상의 연속된 공백 의미
• 단어 역순 추가
  • StringBuilder 단어 추가
• 마지막 공백 제거 & 반환(trim() 사용)

class Solution {
    public String reverseWords(String s) {
        String[] words = s.trim().split("\\s+");
        StringBuilder answer = new StringBuilder();

        for (int i = words.length - 1; i >= 0; i--) {
            answer.append(words[i]).append(" ");
        }

        return answer.toString().trim();
    }
}

결과