151. Reverse words in a string

string

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

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.

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: **If the string data type is mutable in your language, can you solve it in-place with O(1) extra space?

  • code
class Solution {
  public String reverseWords(String s) {
    // remove leading spaces
    s = s.trim();
    // split by multiple spaces
    List<String> wordList = Arrays.asList(s.split("\\s+"));
    Collections.reverse(wordList);
    return String.join(" ", wordList);
  }
}
  • code
class Solution {
    public String reverseWords(String s) {
        String[] l = s.split("\\s+");
        StringBuilder res = new StringBuilder();
        for (int i = l.length - 1; i >= 0; i--){
            // if (!l[i].equals("")) {
                res.append(l[i]);
                res.append(" ");
            // }
        }
        return res.toString().trim();
    }
}
  • code, [::-1] or reversed
class Solution:
    def reverseWords(self, s: str) -> str:
        return " ".join(reversed(s.strip().split()))