4/4/15 - UMD Contest Problems

Today I did two 2013 UMD contest problems: 3 - Guessing Game I and 4 - Tree Isomorphism. Guessing Game I was really easy, and I had already done Tree Isomorphism with Sam on Wednesday and Thursday, but I decided to do it again because Sam did the typing (and most of the thinking) on the last one, and I remembered our approach to the problem well enough to re-solve it. I've noticed that a lot of times I'll read one of these UMD problems and just have no idea what to do, and before talking through it with Sam, Tree Isomorphism was definitely one of those cases where I just had no clue how to approach it.  After seeing the solution once, though, I was able to come up with it again on my own.  I didn't keep track of time, but it probably took about an hour and a half, which isn't very good considering I had already seen the solution once.

One thing about our approach to this problem that confused me and slowed me down was the List<List<TreeNode>> type returned by #permutations(). I couldn't remember our previous solution exactly, so I had to play around with the recursion to get the method to work correctly with the return type. Another thing that threw me off was the choice between List<TreeNode> children and rootNode.children in method arguments. I found that it made the most sense to do the former, because a root node might not always be present, such as when the #permutations() List<List<TreeNode>> was in use. For example, I originally had #treeEquals() take two root nodes and compare children (rather than taking two lists of nodes), but I realized that this would require me to add additional root nodes when all I had was a list of children, such as when checking the permutations of one tree against the other.

I also looked at 5 - Guessing Game II, and it's the same problem—I don't have enough experience to be able to come up with a strategy. I did work through their solution, and I think understand it pretty well, although I wouldn't have been able to come up with that on my own.