Reverse Words in a String Medium 0 attempts
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Reverse Words in a String

Medium StringHash Table LeetCode

You're given a string s made up of words — where a word is any run of non-space characters — separated by spaces. Produce a string containing those words in reverse order, with exactly one space between consecutive words.

Because the input can have leading or trailing spaces and runs of multiple spaces between words, make sure none of that extra spacing survives into the output.

Input Format
Implement reverseWords(s). Inputs below show JavaScript function arguments; there is no stdin parsing.
Output Format
Return the result described in the statement.

Sample Input and Output

Example 1 · Run Sample

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

Example 2

Input
s = "  hello   world  "
Output
"world hello"
Constraints
  • 1 <= s.length <= 10^4
  • s contains English letters, digits, and spaces
Test Cases (2)
Case 1
Args: ["the sky is blue"] Expected: "blue is sky the"
Case 2
Args: [" hello world "] Expected: "world hello"
Topics
StringHash Table

Trim the string, split on one or more whitespace characters to extract words, reverse the array, and join with a single space. The regex split handles multiple consecutive spaces cleanly.

javascript
function reverseWords(s) {
  return s.trim().split(/\s+/).reverse().join(' ');
}

For a more manual approach without built-in reverse:

javascript
function reverseWords(s) {
  const words = [];
  let i = 0;
  while (i < s.length) {
    while (i < s.length && s[i] === ' ') i++;
    if (i >= s.length) break;
    let j = i;
    while (j < s.length && s[j] !== ' ') j++;
    words.push(s.substring(i, j));
    i = j;
  }

  let left = 0, right = words.length - 1;
  while (left < right) {
    [words[left], words[right]] = [words[right], words[left]];
    left++;
    right--;
  }
  return words.join(' ');
}

Time: O(n) — one pass to split, one to reverse. Space: O(n) for the words array.

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JavaScript