static String reverseWords(String input) {
		if (input.length() == 0)
			return "";
		char [] str = input.toCharArray();
		int begin = 0;
		for (int i = 0; i < str.length; i++) {
			if (str[i] == ' ') {
				reverse(str, begin, i-1);
				begin = i + 1;
			}
		}
		reverse(str, begin, str.length-1);
		reverse(str, 0, str.length-1);
		return new String(str);
	}
	static void reverse(char []str, int begin, int end) {
		while(begin < end) {
			char tmp = str[begin];
			str[begin] = str[end];
			str[end] = tmp;
			begin ++;
			end --;
		}
	}