Interview Question for Software Engineer at Salesforce.com:

I used the String.split() function here:

    public static String reverseWords1(String sentence) {
    // Split string at word separators into string and then output from end.
    String[] words = sentence.split(" ");
    StringBuilder result = new StringBuilder();
    for(int i=words.length-1; i>=0; i--)
        result.append(words[i]).append(" ");
    return result.toString();
    }

and here by doing it more the traditional way:

    public static String reverseWords2(String sentence) {
    StringBuilder result = new StringBuilder();
    int lastwordend = sentence.length()-1;
    for (int i = sentence.length()-1; i>=0; i--)
        if (sentence.charAt(i) == ' ') {
        result.append(sentence.substring(i+1, lastwordend+1)+" ");
        lastwordend = i-1;
        }

    return result.toString();
    }

Go backwards through the sentence, looking for delimiters (i.e. space) and collect the word until you find one or run out of string.

private static String reverse(String s){
        if(s == null || s.length() == 1) return s;
        String rvrsd = reverse(s.substring(1)) + s.charAt(0);
        return rvrsd;
    }

It's also possible to use a BreakIterator to break at word boundaries. That way, it can also work in multiple languages, for the win :-)

How about pushing the string on a stack (word by word) ignoring the space character and popping the contents of the stack ?