Advent of Code — Day 6

Don’t we all love lanternfish?

I will be straightforward, my solution is anything but refined.

I want to explain how I did it. First I have a function to define a base set of fish:

function getFishZeroState() {
    return {
        "0" : {"nb": 0, "hatch": false},
        "1" : {"nb": 0, "hatch": false},
        "2" : {"nb": 0, "hatch": false},
        "3" : {"nb": 0, "hatch": false},
        "4" : {"nb": 0, "hatch": false},
        "5" : {"nb": 0, "hatch": false},
        "6" : {"nb": 0, "hatch": false},
        "7" : {"nb": 0, "hatch": false},
        "8" : {"nb": 0, "hatch": false},
    };
}

Could be better? Yes, of course. But I am lazy and I wanted to get it over with without being fancy. I knew the state is not going to change. Ever.

I read the file with the problem input, iterate through it and fill the zero state object as follows:

Input:

3, 4, 3, 1, 2

State:

        "0" : {"nb": 0, "hatch": false},
        "1" : {"nb": 1, "hatch": true},
        "2" : {"nb": 1, "hatch": true},
        "3" : {"nb": 2, "hatch": true},
        "4" : {"nb": 1, "hatch": true},
        "5" : {"nb": 0, "hatch": false},
        "6" : {"nb": 0, "hatch": false},
        "7" : {"nb": 0, "hatch": false},
        "8" : {"nb": 0, "hatch": false},

Code:

Array.from(data.split(','), x => parseInt(x)).forEach( (fish) => {
    fishes[fish]["nb"] += 1;
    fishes[fish]["hatch"] = true;
});

Hatch is just a flag. I will go through that line ONLY if I have to, saving a bit of time.

And when a day passes… I just shift it like this:

Day 1 passes:

        "0" : {"nb": 1, "hatch": true},
        "1" : {"nb": 1, "hatch": true},
        "2" : {"nb": 2, "hatch": true},
        "3" : {"nb": 1, "hatch": true},
        "4" : {"nb": 0, "hatch": false},
        "5" : {"nb": 0, "hatch": false},
        "6" : {"nb": 0, "hatch": false},
        "7" : {"nb": 0, "hatch": false},
        "8" : {"nb": 0, "hatch": false},

Day 2 passes:

        "0" : {"nb": 1, "hatch": true},
        "1" : {"nb": 2, "hatch": true},
        "2" : {"nb": 1, "hatch": true},
        "3" : {"nb": 0, "hatch": false},
        "4" : {"nb": 0, "hatch": false},
        "5" : {"nb": 0, "hatch": false},
        "6" : {"nb": 1, "hatch": true},
        "7" : {"nb": 0, "hatch": false},
        "8" : {"nb": 1, "hatch": true},

Code:

const days = 80;

for(let i = 1; i <= days; i++){
    let newFishes = getFishZeroState();
    for(const fish in fishes){
        if(fishes[fish]["hatch"]){
            if(fish == 0){
                newFishes[8]["nb"] += fishes[fish]["nb"];
                newFishes[8]["hatch"] = true;

                newFishes[6]["nb"] += fishes[fish]["nb"];
                newFishes[6]["hatch"] = true;
            }
            else {
                newFishes[fish-1]["nb"] += fishes[fish]["nb"];
                newFishes[fish-1]["hatch"] = true;
            }
        }
    }
    fishes = newFishes;
}

I just build a new object and replace the old one containing the fish with the new state. Yes, it could’ve been better, I know :D But I didn’t want to complicate it, I wanted to get it done.

And at the end… I just iterate through the fish object and… I sum up the numbers:

let sum = 0;
for(let key in fishes){
    sum += fishes[key]["nb"];
}

Talking time

As of the time and days are as follows:

• I did 10 runs for each and average the times to get the final result

80 days — 0.856ms
256 days — 1.191ms
512 days — 2.741ms
1024 days — 4.293ms
65535 days — 70.004ms
1 gogolplex days — still did not compile :( not efficient enough to get there, even 1 trillion is too much as of now