README_EN.md

151. Reverse Words in a String

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Description

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.

 

Follow up: Could you solve it in-place with O(1) extra space?

Solutions

Python3

class Solution:
    def reverseWords(self, s: str) -> str:
        words = s.strip().split()
        return ' '.join(words[::-1])

Java

class Solution {
    public String reverseWords(String s) {
        List<String> words = Arrays.asList(s.trim().split("\\s+"));
        Collections.reverse(words);
        return String.join(" ", words);
    }
}

C#

public class Solution {
    public string ReverseWords(string s) {
         return string.Join(" ", s.Trim().Split(" ").Where(word => !string.IsNullOrEmpty(word) && !string.IsNullOrEmpty(word.Trim())).Reverse());
    }
}

TypeScript

function reverseWords(s: string): string {
    let words: string[] = s.trim().split(/\s+/g);
    words.reverse();
    return words.join(" ");
}

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