I finished problem A & B in a short period of time, then got stuck in problem C.

To problem C, I was too eager to find a mathematical based optimal solution so that I didn't think of the clear optimization of DFS/BFS.

After a long struggle, I used the brute force & observation method, getting accepted easily.  Although it's somewhat stupid.  But, if you can get good score,  who cares if you found the proof of a pattern?  It was just a failure in strategy.

Wasting too much time on problem C, I had no time to code problem D.

When system test, my problem B just crashed just because a typo of I/O.

Anyway, I love the problemset, nice problems.

Looking forward to the next contest :)