aoc/aoc.cpp

#include <fstream>
#include <vector>
#include <algorithm>
#include <ranges>
#include <numeric>
#include <cmath>
#include <utility>

#include "fmt/format.h"

using levels_t  = std::vector<std::int32_t>;
using reports_t = std::vector<levels_t>;

auto main([[maybe_unused]]int argc, [[maybe_unused]]char const* argv[]) -> int {
    // constexpr auto filename = "./dat/24/ex/02.txt";
    constexpr auto filename = "./tmp.txt";
    std::ifstream strm{filename, std::ios::in | std::ios::binary};
    if (!strm.is_open()) {
        fmt::print("Error opening file: {}\n", filename);
        return 1;
    }

    reports_t reports{};

    levels_t tmp{};
    std::string str{};
    while (strm) {
        auto const c = char(strm.peek());
        if (std::isdigit(c)) {
            str += char(strm.get());
            continue;
        }
        if (c == ' ' && !str.empty()) {
            tmp.emplace_back(std::stoi(str));
            str.clear();
        }
        if (c == '\n' && !str.empty()) {
            tmp.emplace_back(std::stoi(str));
            reports.emplace_back(std::move(tmp));
            str.clear();
        }
        strm.get();
    }

    auto diff = reports | std::views::transform([](auto const& levels) {
        return levels | std::views::adjacent_transform<2>([](auto const& a, auto const& b) {
            return b - a;
        });
    });

    // condition: all increasing or all decreasing.
    auto incdec = diff | std::views::filter([](auto const& levels) {
        auto const n = std::ranges::all_of(levels, [](auto v) { return v < 0; });
        auto const p = std::ranges::all_of(levels, [](auto v) { return v > 0; });
        return n || p;
    });

    // condition: Any two adjacent levels differ by at least one and at most three.
    auto adjdiff = incdec | std::views::filter([](auto const& levels){
        return std::ranges::all_of(levels, [](auto v) {
            return std::abs(v) <= 3;
        });
    });

    auto const safe_reports = std::ranges::distance(adjdiff);

    fmt::print("Part A: {}\n", safe_reports);

    auto lefts = std::views::zip(diff, reports) | std::views::filter([](auto const& pair) {
        auto const& [d, l] = pair;
        auto const n = std::ranges::all_of(d, [](auto v) { return v < 0; });
        auto const p = std::ranges::all_of(d, [](auto v) { return v > 0; });
        return !(n || p);
    }) | std::views::transform([](auto const& pair) {
        auto const& [d, l] = pair;
        return l;
     });

    auto masks = diff | std::views::filter([](auto const& vec) {
        auto const n = std::ranges::all_of(vec, [](auto v) { return v < 0; });
        auto const p = std::ranges::all_of(vec, [](auto v) { return v > 0; });
        return !(n || p);
    }) | std::views::transform([](auto const& vec) {
        auto const p = std::count_if(std::begin(vec), std::end(vec), [](auto const& v) { return v >= 0; });
        auto const n = std::count_if(std::begin(vec), std::end(vec), [](auto const& v) { return v < 0; });
        auto mask = vec | std::views::transform([&](auto const& v) {
                if (p > n) return v >= 0 ? 1 : 0;
                else return v < 0 ? 1 : 0;
            }) | std::ranges::to<std::vector>();
        mask.push_back(1);
        return mask;
    });

    auto const remain_reports = std::views::zip(masks, lefts)
            | std::views::filter([](auto const& pair) {
                auto const& [mask, level] = pair;
                auto const n = std::count_if(std::begin(mask), std::end(mask), [](auto const& v) { return v == 0; });
                return n == 1;
            })
            | std::views::transform([](auto const& pair){
               auto const& [mask, level] = pair;

               return std::views::zip(mask, level) | std::views::filter([](auto const& pair) {
                    auto const& [m, v] = pair;
                    return m == 1;
               }) | std::views::transform([](auto const& pair) {
                    auto const& [m, v] = pair;
                    return v;
               }) | std::ranges::to<std::vector>();
            })
            | std::ranges::to<std::vector>();

    auto rem_diff = remain_reports | std::views::transform([](auto const& vec) {
        return vec | std::views::adjacent_transform<2>([](auto const& a, auto const& b) { return b - a; });
    });

    auto safe_rems_vec = rem_diff | std::views::transform([](auto const& vec) {
        return vec | std::views::filter([](auto const& a) {
            return std::abs(a) <= 3;
        }) | std::ranges::to<std::vector>();
    }) | std::ranges::to<std::vector>();

    auto safe_rems = safe_rems_vec | std::views::filter([](auto const& vec) {
        return vec.size() > 0;
    }) | std::views::filter([](auto const& vec) {
        auto const n = std::ranges::all_of(vec, [](auto v) { return v < 0; });
        auto const p = std::ranges::all_of(vec, [](auto v) { return v > 0; });
        return n || p;
    });

    auto const safe_reports_rem = std::ranges::distance(safe_rems);

    // for (auto rep : safe_rems) {
    //     for (auto v : rep) {
    //         fmt::print("{} ", v);
    //     }
    //     fmt::print("\n");
    // }
    fmt::print("Part B: {}\n", safe_reports + safe_reports_rem);

    return 0;
}