My Advent of Code 2021 solutions written in C++

day01.cpp

#include <algorithm>
#include <fstream>
#include <iostream>
#include <ranges>
#include <string>

void part1() {
    std::ifstream input{"input.txt"};
    auto view = std::ranges::istream_view<int>(input);

    int previous = *view.begin();
    int count = 0;

    for (auto depth : view) {
        /* Load previous depth and store current depth as next round's previous. */
        auto previous_depth = depth;
        std::swap(previous, previous_depth);

        /* We increment count when the depth increased from the previous round. */
        if (previous_depth < depth) {
            count += 1;
        }
    }

    std::cout << count << " measurements are larger than the previous measurement!\n";
}

void part2() {
    std::puts("Check back when ranges don't suck anymore in C++23.");
}

int main() {
    part1();
    part2();

    return 0;
}

day02.cpp

#include <charconv>
#include <fstream>
#include <iostream>
#include <ranges>
#include <string>
#include <string_view>

constexpr std::string_view g_whitespace{" "};

void part1() {
    std::ifstream input{"input.txt"};

    int horizontal = 0;
    int depth = 0;

    for (std::string line; std::getline(input, line); /* ... */) {
        /* Split each line at the whitespace. */
        auto split = std::views::transform(std::views::split(line, g_whitespace), [](auto s) {
            return std::string_view(s.begin(), s.end());
        });

        /* Extract the command and parse the `X` value into an integer. */
        const auto command = *split.begin();
        int amount{};
        {
            const auto amount_str = *std::ranges::next(split.begin());
            std::from_chars(amount_str.data(), amount_str.data() + amount_str.size(), amount);
        }

        /* Process the command. */
        if (command == "forward") {
            horizontal += amount;
        } else if (command == "down") {
            depth += amount;
        } else if (command == "up") {
            depth -= amount;
        }
    }

    std::cout << horizontal * depth << " is the final position!\n";
}

void part2() {
    std::ifstream input{"input.txt"};

    int horizontal = 0;
    int depth = 0;
    int aim = 0;

    for (std::string line; std::getline(input, line); /* ... */) {
        /* Split each line at the whitespace. */
        auto split = std::views::transform(std::views::split(line, g_whitespace), [](auto s) {
            return std::string_view(s.begin(), s.end());
        });

        /* Extract the command and parse the `X` value into an integer. */
        const auto command = *split.begin();
        int amount{};
        {
            const auto amount_str = *std::ranges::next(split.begin());
            std::from_chars(amount_str.data(), amount_str.data() + amount_str.size(), amount);
        }

        /* Process the command. */
        if (command == "forward") {
            horizontal += amount;
            depth += amount * aim;
        } else if (command == "down") {
            aim += amount;
        } else if (command == "up") {
            aim -= amount;
        }
    }

    std::cout << horizontal * depth << " is the final position!\n";
}

int main() {
    part1();
    part2();

    return 0;
}