Reflexive Position
This is the third time we see this number?
Champernowne’s constant. The first time we see it is in problem 40. If you take a look, you can feel the difference between the problems created in recent years and the problems created 10 years ago.
This problem is really interesting. It is easy to write a brute force code for small numbers, it is no-brainer! But for large numbers, it takes hours or days to get a correct answer.
From a long time ago, I knew how to solve it, but I do not want to write the complicated code to handle all situations. Several days ago, I decided to work on this problem in my spare time. It is really disturbing to find bugs here and there. Finally, I made it work. It takes less than 1 ms to get the answer! But I spent hours to make it correct.
The examples are very helpful if one does not write his own brute force code. 7780 is a very very important number. Even with this number, I still made some mistake in my code. But I watched those 3^n for a couple of minutes, then figured out why my answer is not correct. Another important number is 243, but it is small and easy to debug.
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