Reverse Words in a String

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Given a string s, reverse the order of words. Multiple spaces between words should be reduced to a single space. Leading/trailing spaces should be removed.

Example 1
Input: "the sky is blue" → Output: "blue is sky the"
Example 2
Input: " hello world " → Output: "world hello"

Solution Approach

Split by spaces, filter empty strings, reverse the list, join with single space.

  • Use built-in split or manual two-pointer approach.
  • Trim the string, split on whitespace (handles multiple spaces).
  • Reverse the resulting array.
  • Join with single space.
Java
class Solution {
    public String reverseWords(String s) {
        String[] words = s.trim().split("\\s+");
        int lo = 0, hi = words.length - 1;
        while (lo < hi) {
            String tmp = words[lo]; words[lo] = words[hi]; words[hi] = tmp;
            lo++; hi--;
        }
        return String.join(" ", words);
    }
}
  • Time Complexity: O(N)
  • Space Complexity: O(N)