AoC 2019 D13: Care Package

C++ | Problem statement | Source code | Tags: IntcodeArcade game

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Part 1

For part 1, we just run to completion and pop all outputs:

int block_count = 0;
std::vector<long long> outputs = prog.pop_all_output();
for (int i = 2; i < outputs.size(); i += 3) {
    long long tile_id = outputs[i];
    if (tile_id == 2) {
        block_count++;
    }
}
cpp

Part 2

Now, building on day 11, the Intcode program is interactive but produces many outputs at a time, so we cannot use a fixed number of run_until_output() calls. Instead, I added a run_until_input() method that runs until an input is needed, at which point we are certain that all outputs have been produced.

Initially, I thought about just playing the game myself, but it turned out to be a quite tedious process. Reddit wisdom suggested two ways: (1) always move the paddle towards the ball, or (2) hack the memory to replace the paddle's row with walls. I implemented (1) since it felt more satisfying.

while (true) {
    prog.run_until_input();
    int ball_pos;
    int paddle_pos;
    int score;
    std::vector<long long> outputs = prog.pop_all_output();
    // ...Process output
    if (prog.halted) {
        std::cout << score << std::endl;
        break;
    }
    if (ball_pos < paddle_pos) {
        input = -1;
    } else if (ball_pos > paddle_pos) {
        input = 1;
    } else {
        input = 0;
    }
    prog.send_input(input);
    prog.step();
}
cpp

I still kept my visualization logic though, and it was fun to watch the AI play the game:

Game intelligence playing breakout

(One complaint: I didn't understand from the problem statement that each time only the diff is output, so at first I rendered the entire screen each time and wondered why the blocks disappeared!)

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