151. Reverse Words in a String

Reverse Words in a String

Problem 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.

 

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?

function reverseWords(s) {
  const ret = [];
  let word = [];
  for (let i = 0; i < s.length; ++i) {
    if (s.charAt(i) === ' ') {
	    // We found the space, put word in front (if there is any)
        word.length > 0 && ret.unshift(word.join(''));
		// Reset the current word
        word = [];
      }
    else {
	  // Add characters to the current word
      word.push(s.charAt(i));
    }
  }
  // If there is current word exists, add it in front
  word.length > 0 && ret.unshift(word.join(''));
  return ret.join(' ');
};

OR

/**
 * @param {string} s
 * @return {string}
 */

var reverseWords = function(s) {
    let splitted =s.trim().split(" ").filter((val)=>val!='');
    return splitted.reverse().join(" ");
};

OR

return s.trim().split(/[ ]+/).reverse().join(" ");

Conclusion

That’s all folks! In this post, we solved LeetCode problem 151. Reverse Words in a String

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Happy coding!