LeetCode-151.Reverse Words in a String

Given an input string, reverse the string word by word.

For example,
Given s = "the sky is blue",
return "blue is sky the".

Update (2015-02-12):
For C programmers: Try to solve it in-place in O(1) space.

Clarification:

• What constitutes a word?
  A sequence of non-space characters constitutes a word.
• Could the input string contain leading or trailing spaces?
  Yes. However, your reversed string should not contain leading or trailing spaces.
• How about multiple spaces between two words?
  Reduce them to a single space in the reversed string.

public string ReverseWords(string s)
        {
            string[] ss = s.Trim().Split(' ');
            string result = "";
            for (int i = ss.Length - 1; i >= 0; i--)
            {
                if (ss[i] != "")
                    result += ss[i] + " ";
            }
            return result.TrimEnd();
        }

public string ReverseWords(string s)
        {
            string[] ss = s.Trim().Split(' ');
            StringBuilder result = new StringBuilder();
            for (int i = ss.Length - 1; i > 0; i--)
            {
                if (ss[i] != "")
                    result.Append(ss[i]+" ");
            }
            return result.Append(ss[0]).ToString();
        }