[philiplu]

One other thing - can't believe I forgot to mention this: once you solve a problem, read the solvers' thread in the forum! I learned so much by doing that, which fed into success on later problems. The link will be at the bottom of the problem page once you've solved it.

There are some much later problems where some obscure technique gets mentioned, even though the problem is doable without that technique. But then later on, there are other problems where that technique is practically required. I can think of multiple 100% difficulty problems which were actually much easier than that for me, because I had already seen and tried out the techniques that enable a fast solution.

And sorry, not going to mention any of those techniques. A lot of the fun I have in solving PE problems is that incremental increase in knowledge as time goes on.