The map glitch, I know about it - I use it to cheat, I will take it out when the scoring and finite number of lives is implemented. If you come across a room with pop up mines they are not frozen by the glitch, but their bullets are which is kinda funny, I will let one chase me around a room and I will drop frozen fireballs every where and then I will tap the 'M' key and watch the fire works.

I have thought about making a save feature - I have never used it before so I have to look at some other people's scenarios to figure it out. To save a room would only require 16 bits, 5 bits would be required per room to keep track of the keys, then it would only take 1 bit to say if the rooms was visited or not. we are looking at a save file that is less than 2K. The colored zone work this way, a key will sit in the middle of a 9 red square pattern, around the 9 squares is a 2 square thick yellow zone. Red zones can over lap, so by looking at the map you will get an idea of where the keys are, if you find a stretch of red rooms more than 4 you know several (2 or more) keys are close by. Have you found the exit portal room yet? I have to make a save feature and another feature to have a list of people who have escaped.

I would think that not letting them block the intersection would do a huge amount, then resolve a 4 way stop by who ever can go and was waiting the longest.

Merge sort is one of my favorites. Never tried implementing it in Java, only in C and Pascal. Might be cool to illustrate a balanced tree like an AVL or Red/Black tree (or maybe even a 2-3 tree).