hiepph/advent-of-code-2019

Advent of Code 2019

This year is entertaining since I get to build a computer that interprets integer codes. Kudos to the people who involved to make it educational.

I use Java for this year with OOP style to encapsulate layers of abstractions and functionalities. It fits perfectly.

Code for the first days are terrible since I wanted to finish the challenges quickly, but I refined a lot along the way. I had to refactor and add unit tests since the latter challenges require the previous computer module.

Day 9

• I keep getting this annoying 203 diagnostic code error:

  • Refer: reddit.
  • Parameters that an instruction writes to will never be in immediate mode.

• StackOverflow error:

  • Switched to iterative mode instead of recursion mode:

// bad 
computer.execute(inputCode);

void execute() { 
    // ...
    execute();
}

// fixed
while (!computer.isHalted()) {
  computer.execute(inputCode);
}

Day 12

x, y, and z coordinates are independent of each other -> find the cycles in each of three axis. The answer is the least common multiple (LCM) of three cycles.

• Reference:
  • https://0xdf.gitlab.io/adventofcode2019/12

Day 13

Visualisation to understand part 2: reddit

I have to refactor the IntCodeComputer class again in this challenge.

1. Add an input queue of input code:

// old
public long execute(int inputCode) { }

// new
private Queue<Integer> inputs;

public void addInput(int inputCode) {
    inputs.add(inputCode);
}

public void execute() { }

It makes more sense since we don't need inputCode for each execution. execute() now will run continuously until it halts or runs out of input stream.

2. Add an output queue of diagnostic code:

// old
public long execute(int inputCode) { }
    
// new    
private Queue<Integer> outputs;

public Queue<Integer> getOutputs() {
    return outputs;
}

In this way, instead of external polling for each output, I can gather all output at once.

// old
int x = (int) computer.execute(inputCode);

// new
while (!outputs.isEmpty()) {
    int x = outputs.remove();
    // ...
}

Day 14

• Part 1: Have 2 dictionaries of needs and exists and continually update values from them, starting from ("FUEL", 1).

Map<String, Integer> exists = new HashMap<>();
Map<String, Integer> needs = new HashMap<>();
needs.put("FUEL", 1);

The buggy parts I encountered is to update the value of those dictionaries:

exists.put(need, exists.getOrDefault(need, 0) + numReactions * productQuantity - needQuantity);
needs.put(reactant.name(),needs.getOrDefault(reactant.name(), 0) + reactant.quantity() * numReactions);

• Reference