public static String capitalizeFirstLetters(String s)
	{
		/*
		 * Please implement this method to capitalize all first letters of the words in the given String. 
		 * All other symbols shall remain intact. If a word starts not with a letter, it shall remain intact too. 
		 * Assume that the parameter String can only contain spaces and alphanumeric characters. 
		 * NOTE: please keep in mind that the words can be divided by single or multiple spaces. 
		 * The spaced also can be found at the beginning or the end of the parameter string, 
		 * and you need to preserve them.
		 */
		
		if(s ==null ||s.isEmpty()){
			return "";
		}
		StringBuilder sb = new StringBuilder();
		s.toUpperCase();
		int length = s.length();
		boolean mark = true;//mark if processing a new word
		for (int i = 0; i < length; i++) {
			char c = s.charAt(i);
			if(Character.isLetter(c)){
				if(mark){
					c = Character.toUpperCase(c);
					mark = false;
				}
			}else{//end of current word!
				mark = true;
			}
			sb.append(c);
		}
		return sb.toString();
	}