🎄 Advent of Code 2'023 - Day 06

Published data: 6 December 2023

Day 06: Wait For It

* Cf. aoc. d. vi xxiii

Today’s challenge was surprisingly easy in comparison to the previous ones.

The problem involves participating in toy boat races with a fixed time limit. The goal is to maximize the distance traveled by adjusting the time the boat’s button is held down at the start. The races have different durations and existing record distances. The challenge is to calculate the number of ways the boat can beat the record in each race and find the product of these values.

We have a simple input that looks like this:

Time:      7  15   30
Distance:  9  40  200

The first line is the time limit of the race. The distance is the record distance for the above race.

Parsing The Input

* using int64 = long long;

We have very few numbers as the input, so we don’t really need to do any parsing. I just added it to a vector of int64 * and I’m good to go.

vector<long long> A = { {61, 67, 75, 71}, {430, 1036, 1307, 1150} };

PARS I

The only thing we need to figure out is the math behind the problem. If you spend n seconds holding the button down, the boat will travel n * (time - n) distance. If this value is greater than the record distance, the boat will beat the record. We just need to find the number of ways to do this.

static int64 solve(const vector<int64> &times, const vector<int64> &distance) {
    vector<int64> A;
    for (int i = 0; i < times.size(); ++i) {
        int64 ans = 0;
        int64 n = 1;
        while (n < times[i]) {
            if ((n * (times[i] - n)) > distance[i]) ans++;
            n++;
        }
        A.push_back(ans);
    }

    int64 ans = 1;
    for (const int64 &i: A) ans *= i;

    return ans;
}

Here is a gift: 🌟

PARS II

Surprisingly, part two can be solved using the same code as part one. We just need to change the input. I’ve encapsulated the previous logic in the solve function, so I just need to call it with the new input.

public:
    static int64 part1() {
        return solve({61, 67, 75, 71}, {430, 1036, 1307, 1150});
    }

    static int64 part2() {
        return solve({61677571ll}, {430103613071150ll});
    }

We got them 🌟🌟