day14notes.txt

# Part 1

Let's get parsing done quickly today.

Parsing done in 30 minutes, not so bad.

Now, it looks like the naive approach may work for part 1, but will
probably blow up one they ask for say 1000 steps. Let's try it anyway.

Hmm, I want to store rules in a lookup table rather than my current list.

Argh, @print doesn't correctly print empty strings 🤦

One more hour debugging an inverted STA. And I'm finally realizing I'm
headed into a wall: even for the sample, the polymer contains more than
3000 elements.

In fact, can I predict the final length of the polymer? If every pair
of elements has an element inserted inside, a length 4 polymer becomes
a length 7 polymer, which becomes a length 13 polymer… each element
except the last has a new neighbor.

  L(n) = 2*(n-1) + 1 = 2*n - 1
  L(4) = 7
  L(7) = 13
  L(13) = 25
  …

A quick spreadsheet gives:
  4
  7
  13
  25
  49
  97
  193
  385
  769
  1537
  3073

My input has 20 elements.
  20
  39
  77
  153
  305
  609
  1217
  2433
  4865
  9729

Hmm, 9729 bytes (0x2601) does fit in memory. But I'm pretty sure I'll have to 
change my approach for the next part.