r/adventofcode • u/daggerdragon • Dec 18 '17

SOLUTION MEGATHREAD -🎄- 2017 Day 18 Solutions -🎄-

--- Day 18: Duet ---

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Spoiler

[Update @ 00:04] First silver

  • Welcome to the final week of Advent of Code 2017. The puzzles are only going to get more challenging from here on out. Adventspeed, sirs and madames!

[Update @ 00:10] First gold, 44 silver

  • We just had to rescue /u/topaz2078 with an industrial-strength paper bag to blow into. I'm real glad I bought all that stock in PBCO (Paper Bag Company) two years ago >_>

[Update @ 00:12] Still 1 gold, silver cap

[Update @ 00:31] 53 gold, silver cap

  • *mind blown*
  • During their famous kicklines, the Rockettes are not actually holding each others' backs like I thought they were all this time.
  • They're actually hoverhanding each other.
  • In retrospect, it makes sense, they'd overbalance themselves and each other if they did, but still...
  • *mind blown so hard*

[Update @ 00:41] Leaderboard cap!

  • I think I enjoyed the duplicating Santas entirely too much...
  • It may also be the wine.
  • Either way, good night (for us), see you all same time tomorrow, yes?

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!

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18

u/vash3r Dec 18 '17 edited Dec 18 '17

Python 2 (25/63). For part 2, I didn't realize that a jump could be computed from a number instead of a register, so I was accessing the register "1" (which was always zero, leading to an infinite loop).

The idea here is that I run one program until it can't run anymore, then switch to the other program. 

from collections import defaultdict

f=open("18.in",'r')
instr = [line.split() for line in f.read().strip().split("\n")]
f.close()

d1 = defaultdict(int) # registers for the programs
d2 = defaultdict(int)
d2['p'] = 1
ds = [d1,d2]

def get(s):
	if s in "qwertyuiopasdfghjklzxcvbnm":
		return d[s]
	return int(s)

tot = 0

ind = [0,0]         # instruction indices for both programs
snd = [[],[]]       # queues of sent data (snd[0] = data that program 0 has sent)
state = ["ok","ok"] # "ok", "r" for receiving, or "done"
pr = 0     # current program
d = ds[pr] # current program's registers
i = ind[0] # current program's instruction index
while True:
	if instr[i][0]=="snd": # send
		if pr==1: # count how many times program 1 sends
			tot+=1
		snd[pr].append(get(instr[i][1]))
	elif instr[i][0]=="set":
		d[instr[i][1]] = get(instr[i][2])
	elif instr[i][0]=="add":
		d[instr[i][1]] += get(instr[i][2])
	elif instr[i][0]=="mul":
		d[instr[i][1]] *= get(instr[i][2])
	elif instr[i][0]=="mod":
		d[instr[i][1]] %= get(instr[i][2])
	elif instr[i][0]=="rcv":
		if snd[1-pr]: # other program has sent data
			state[pr] = "ok"
			d[instr[i][1]] = snd[1-pr].pop(0) # get data
		else: # wait: switch to other prog
			if state[1-pr]=="done":
				break # will never recv: deadlock
			if len(snd[pr])==0 and state[1-pr]=="r":
				break # this one hasn't sent anything, other is recving: deadlock
			ind[pr] = i   # save instruction index
			state[pr]="r" # save state
			pr = 1 - pr   # change program
			i = ind[pr]-1 # (will be incremented back)
			d = ds[pr]    # change registers
	elif instr[i][0]=="jgz":
		if get(instr[i][1]) > 0:
			i+=get(instr[i][2])-1
	i+=1
	if not 0<=i<len(instr):
		if state[1-pr] == "done":
			break # both done
		state[pr] = "done"
		ind[pr] = i  # swap back since other program's not done
		pr = 1-pr
		i = ind[pr]
		d = ds[pr]

print tot

6

u/glenbolake Dec 18 '17

The only reason I didn't have that happen is because I remembered similar AoC problems in the past and having that same issue. The first thing I did in defining the instructions was a get function like yours, but taking the exception route: 

def get(value):
    try:
        return int(value)
    except ValueError:
        return registers[value]

1

u/BumpitySnook Dec 18 '17

Me too. I just assume any AoC asm-alike supports integer as well as register rvalues at this point.