Reverse words in a string

Hi folks,

I am here with another example, how to reverse words in a string or sentence?

I have tried with a approach. I would welcome other approaches, please share..

////// Complexity: O(n) + O(n)/2 ~ O(n)

public static string ReverseWordsInString(string str)
        {
            string reverse = ReverseString(str);
            string temp = "";
            foreach (string s in reverse.Split(' '))
            {
                temp += ReverseString(s) + ' ';
            }

            return temp;
        }

private static string ReverseString(string str)
        {
            char[] chars = str.ToCharArray();
            int j = str.Length-1;

            for (int i = 0; i<str.Length/2; i++)
            {
                char c = chars[i];
                chars[i] = chars[j];
                chars[j] = c;      
                j--;
            }
            return new string(chars);
        }