Advent of code - Day 8

Are you participating in the Advent of code this year?

If you don't know what the advent of code is, it's a website where you'll find a daily challenge (every day it gets harder). It's a really fun event, you should participate!

I try to solve the exercises using either JavaScript or TypeScript and will share my solutions daily (with one day delay so no one can cheat!). I only share the solution for the second part.

When I saw the exercise for day #8, I really though "oh boy, this one is going to be hardcore". I thought we'd need to implement a runtime for their weird assembly-like language. Lucky for us, this was way easier than what I assumed!

I basically just wrote a function that determines if the program exits successfully or not, and then run it agains every possible version of the assembly-like code. Here is what it looks like:

const SUCCESS = "SUCCESS";
const ERROR = "ERROR";

// Runs the program, and return SUCCESS or ERROR
// Depending on whether or not it finished (line number > code.length)
function runProgram(code) {
  // If a line is processed 2 times, it's an error
  const alreadyProcessed = [];
  let global = 0;
  let currentLine = 0;

  while (true) {
    if (alreadyProcessed[currentLine] === true) return { global, status: ERROR, alreadyProcessed };
    if (code[currentLine] === undefined)
      return { global, status: SUCCESS, alreadyProcessed };
    alreadyProcessed[currentLine] = true;
    const [inst, argument] = code[currentLine];
    switch (inst) {
      case "acc":
        global += parseInt(argument, 10);
        currentLine += 1;
        break;
      case "jmp":
        currentLine += parseInt(argument, 10);
        break;
      case "nop":
        currentLine += 1;
        break;
      default:
        throw new Error(inst);
    }
  }
}

// Let's just bruteforce, and run the program changing any
// line that is a nop or a jmp to find which one is corrupted
input.forEach((_value, index) => {
  const code = [...input];
  const [inst, argument] = code[index];
  if (inst === "jmp") code[index] = ["nop", argument];
  else if (inst === "nop") code[index] = ["jmp", argument];
  const altResult = runProgram(code);
  if (altResult.status === "SUCCESS") console.log(altResult);
});

Feel free to share your solution in the comments!

Photo by Markus Spiske on Unsplash

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Advent of code - Day 8

Quentin Ménoret

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