public static boolean isAllUnique(String s) {
		if	( s.length() > 256 ) return false;
		
		// by default, all values in boolean array are set to #f
		boolean[]	charSet = new boolean[256];
		for (int i=0 ; i != s.length(); ++i ) {
			int		c  =  s.charAt(i);
			if ( charSet[c] ) {
				return false;
			}
			charSet[ c ] = true;
		}
		return true;
	}