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

Medium StringHash Table LeetCode

Given a string s, reverse the order of the words. A word is a sequence of non-space characters. Return the words in reverse order, separated by a single space.

The input may have leading/trailing spaces and multiple spaces between words. The output should have no extra spaces.

Examples

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

Input: s = "  hello world  "
Output: "world hello"

Input: s = "a good   example"
Output: "example good a"

Constraints

  • 1 <= s.length <= 10^4
  • s may contain leading or trailing spaces and multiple spaces between words.
Sample Input
s = "the sky is blue"
Sample Output
"blue is sky the"
Constraints
  • 1 <= s.length <= 10^4
  • s contains English letters, digits, and spaces
Test Cases
Case 1
Args: ["the sky is blue"] Expected: "blue is sky the"
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.

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

For a more manual approach without built-in reverse:

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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