[leetcode #151] Reverse Words in a String

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 1:

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

Example 2:

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

Example 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.

Example 4:

Input: s = "  Bob    Loves  Alice   "
Output: "Alice Loves Bob"

Example 5:

Input: s = "Alice does not even like bob"
Output: "bob like even not does Alice"

Constraints:

・ 1 <= s.length <= 104
・ s contains English letters (upper-case and lower-case), digits, and spaces ' '.
・ There is at least one word in s.

Idea

java에서 지원하는 string library를 사용하면 별 생각 안 하고 풀 수 있는 문제다.

우선 string을 regex를 이용해 빈 공간을 splitator로 쓰면 string이 자동적으로 분리된다. 분리된 string을 역순으로 해서 string builder에 집어넣어준 뒤 string의 가장 뒤에 space 하나를 넣어준다. 마지막에는 trim을 호출해 앞 뒤 공간에 있는 빈 공간을 제거하면 된다.

library를 쓰면 너무나 간단한 문제라 문제에 대한 평가가 좋지 않다.

바쁜 와중이라 이렇게 쉬운 문제가 나온 것이 다행이다.

Solution

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

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

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

Reference

https://leetcode.com/problems/reverse-words-in-a-string/