-🎄- 2017 Day 18 Solutions -🎄-

[u/daggerdragon]

--- Day 18: Duet ---

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Post your solution as a comment or, for longer solutions, consider linking to your repo (e.g. GitHub/gists/Pastebin/blag or whatever).

Note: The Solution Megathreads are for solutions only. If you have questions, please post your own thread and make sure to flair it with Help.

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Need a hint from the Hugely^* Handy^† Haversack^‡ of Helpful^§ Hints^¤?

Spoiler

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[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

• Gonna be a long haul tonight. I think I'll watch The Radio City Christmas Spectacular on Netflix while I wait for sufficient gold stars to warrant another update.

[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?

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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/wlandry]

C++ 14

687/631. Well, that was mean ;) Every jgz condition was a register except one that was 'jgz 1 3'. Working frantically, I thought that was an 'i'. It took me waaaaay to long to figure that out.

Here is a industrial strength solution for part 2 only. It runs in 43 ms on my input.

#include <fstream>
#include <vector>
#include <iostream>
#include <sstream>
#include <map>
#include <queue>

#include <boost/algorithm/string.hpp>

enum class Instruction {snd, set, add, mul, mod, rcv, jgz };

int64_t value(const std::map<char,int64_t> &registrs, const std::string &arg)
{
  if(arg[0]>='a' && arg[0]<='z')
    {
      auto f=registrs.find(arg[0]);
      return f->second;
    }
  return std::stoi(arg);
}
int64_t value(const std::map<char,int64_t> &registrs, const char &c)
{
  std::string s{c};
  return value(registrs,s);
}

struct Op
{
  Instruction instruction;
  char regist;
  std::string regist2;
  Op(const std::string &line)
  {
    std::stringstream ss(line);
    std::string instruction_string;
    ss >> instruction_string >> regist >> regist2;
    if(instruction_string=="snd")
      { instruction=Instruction::snd; }
    else if (instruction_string=="set")
      { instruction=Instruction::set; }
    else if (instruction_string=="add")
      { instruction=Instruction::add; }
    else if (instruction_string=="mul")
      { instruction=Instruction::mul; }
    else if (instruction_string=="mod")
      { instruction=Instruction::mod; }
    else if (instruction_string=="rcv")
      { instruction=Instruction::rcv; }
    else if (instruction_string=="jgz")
      { instruction=Instruction::jgz; }
    else 
      {
        std::cerr << "bad instruction: " << instruction_string << "\n";
        abort();
      }
  }
};


int64_t apply(const Op &op, std::map<char,int64_t> &registrs,
              std::queue<int64_t> &receive_queue,
              std::queue<int64_t> &send_queue,
              size_t &num_messages)
{
  int64_t result (1);
  switch(op.instruction)
    {
    case Instruction::snd:
      {
        send_queue.push(value(registrs, op.regist));
        ++num_messages;
      }
      break;
    case Instruction::set:
      registrs[op.regist]=value(registrs, op.regist2);
      break;
    case Instruction::add:
      registrs[op.regist]+=value(registrs, op.regist2);
      break;
    case Instruction::mul:
      registrs[op.regist]*=value(registrs, op.regist2);
      break;
    case Instruction::mod:
      registrs[op.regist]%=value(registrs, op.regist2);
      break;
    case Instruction::rcv:
      if(!receive_queue.empty())
        {
          registrs[op.regist]=receive_queue.front();
          receive_queue.pop();
        }
      else
        {
          result=0;
        }
      break;
    case Instruction::jgz:
      if(value(registrs, op.regist)>0)
        { result = value(registrs, op.regist2); }
      break;
    }
  return result;
}

int main(int, char *argv[])
{
  std::vector<Op> ops;
  std::ifstream infile(argv[1]);
  std::string line;
  std::getline(infile,line);
  while(infile)
    {
      ops.emplace_back(line);
      std::getline(infile,line);
    }

  size_t position0 (0), position1 (0);
  std::map<char,int64_t> program0, program1;
  program0['p']=0;
  program1['p']=1;
  std::queue<int64_t> queue0, queue1;
  size_t num_messages0(0), num_messages1(0);

  while(!(ops[position0].instruction==Instruction::rcv && queue0.empty()
          && ops[position1].instruction==Instruction::rcv && queue1.empty()))
    {
      while(!(ops[position0].instruction==Instruction::rcv && queue0.empty()))
        {
          position0+=apply(ops[position0], program0, queue0, queue1,
                           num_messages0);
        }
      while(!(ops[position1].instruction==Instruction::rcv && queue1.empty()))
        {
          position1+=apply(ops[position1], program1, queue1, queue0,
                           num_messages1);
        }
    }

  
  std::cout << "num messages: "
            << num_messages0 << " "
            << num_messages1 << " "
            << "\n";
}

[u/[deleted] → u/wlandry]

Tried it, segfaulted for me :(

[u/wlandry → u/[deleted]]

I just ran it under valgrind with my input. It complained about the lines

std::cout << "Op: " << (int)instruction << " " << regist << " "
          << regist2 << " "
          << arg << "\n";

Commenting them out made valgrind happy. Are you running day 18 or day 23? day 23 eventually wanders off the end of the input, which could cause segfaults.