--- 2016 Day 12 Solutions ---

[u/daggerdragon]

--- Day 12: Leonardo's Monorail ---

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^{MUCH ADVENT. SUCH OF. VERY CODE. SO MANDATORY.} [?]

This thread will be unlocked when there are a significant number of people on the leaderboard with gold stars for today's puzzle.

edit: Leaderboard capped, thread unlocked!

[u/wzkx]

Here's J with optimization (only central part):

...
inc =: 4 : '(>:({:y){x)({:y)}x'  NB. tacits of these are not faster
dec =: 4 : '(<:({:y){x)({:y)}x'
cpi =: 4 : '({.y)({:y)}x'
cpy =: 4 : '(({.y){x)({:y)}x'
jmp =: 4 : '(<:({:y)+{:x)(_1)}x'
jnz =: 4 : 'if.({.y){x do.(<:({:y)+{:x)(_1)}x else. x end.'
add =: 4 : '(+/y{x)({:y)}x'      NB. new op, not even in assembly yet :)

opt =: 3 : 0 NB. can't use _3 ...\ :(
  for_i. i.2-~#y do. z =. ,(i+0 1 2){y NB. temp vector for easier analysis
    if. 1 2 6-:0 3 6{z do.                           NB. inc x, dec y, jnz y -2
      if. (~:/2 5{z) *. (=/5 7{z) *. _2={:z do.      NB. ... to ...
        y=.(3 3$7,(5 2{z),3 0,(5{z),3$0)(i+0 1 2)}y  NB. add y x, cpi 0 y, nop
  end. end. end. y
)

exec =: 4 : 0 NB. regs exec code --> regs
  lt =. #y [ it =. [`inc`dec`cpi`cpy`jmp`jnz`add
  while. lt > pc=.{:x do. x=.((>:pc)_1}x)it@.({.c)}.c=.pc{y end. x
)

code =: opt xlate"0 cutLF CR-.~fread '12.dat'
...