public String replace(String newWord, int pos, char ch) {
        StringBuffer buffer = new StringBuffer();
        buffer.append(newWord.substring(0, pos));
        buffer.append(ch);
        buffer.append(newWord.substring(pos+1,newWord.length()));
        return buffer.toString();
    }
150s qs 18.10
Given two words of equal length in dictionary convert one word to another one letter at a time
in such a way that all intermediate words are int the dictionary
src/com/interview/graph/ConvertOneWordToAnother.java