By running Ladders.java I discovered that it is not possible to change just one letter in the word "aargh" to obtain a different legal 5-letter English word. You can run Ladders.java yourself and discover this. In other words, "aargh" is an isolated vertex in the ladders graph (i.e., it has no neighbors).
Add code to the main method in Ladders.java to printout all isolated vertices (legal 5-letter words) in the ladders graph. Also, printout the number of such isolated vertices.
Note that once you have this set of words you can always stump your friend in the ladders word game!