aoc25/day2/main.cpp

#include <algorithm>
#include <expected>
#include <fstream>
#include <iostream>
#include <print>
#include <ranges>
#include <string>
#include <string_view>
#include <unordered_map>
#include <vector>

struct IDRange {
    long leftRange;
    long rightRange;
};

auto parseRanges(const std::string &filename) -> std::expected<std::vector<IDRange>, std::string> {
    std::ifstream inputF{filename};

    if (!inputF) {
        return std::unexpected{"Some file open error.\n"};
    }
    std::vector<IDRange> idRanges{};

    std::string bigString{};
    std::getline(inputF, bigString);
    auto ranges = std::ranges::to<std::vector<std::string>>(std::views::split(bigString, ','));

    for (const auto &range : ranges) {
        auto subParts = std::ranges::to<std::vector<std::string>>(std::views::split(range, '-'));
        idRanges.emplace_back(std::stol(subParts[0]), std::stol(subParts[1]));
    }

    inputF.close();

    return std::move(idRanges);
}

auto countDoubles(const std::vector<IDRange> &idRanges) {
    long doubles{};
    for (const auto &rng : idRanges) {
        // std::println("{}-{}", rng.leftRange, rng.rightRange);
        for (long i = rng.leftRange; i <= rng.rightRange; i++) {
            auto str_version = std::to_string(i);
            auto str_len = str_version.size();
            // std::print("Checking {}. Length: {}", str_version, str_version.size());
            if (str_len % 2 == 0) {
                // std::print(" Divisible by two, splitting...");
                std::string_view left_half = std::string_view(str_version).substr(0, str_len / 2);
                std::string_view right_half = std::string_view(str_version).substr(str_len / 2, str_len);
                // std::print("Halves: {}/{}",left_half, right_half);
                if (left_half == right_half) {
                    // std::print(" EQUAL!");
                    doubles += i;
                }
            }
            // std::println();
        }
    }
    return doubles;
}

auto calculatePossibleSplits(int length) -> std::vector<int> {
    // std::println("Possible ways to split a str of length {}: ", length);
    std::vector<int> returnVec{};
    for (auto toCheck : std::views::iota(2, length + 1)) {
        if (length % toCheck == 0) {
            // std::println("{}", toCheck);
            returnVec.push_back(toCheck);
        }
    }
    return std::move(returnVec);
}
std::unordered_map<int, std::vector<int>> splitMap{};
auto getPossibleSplits(int length) -> const std::vector<int> & {
    if (!splitMap.contains(length)) {
        // std::println("Caching {}",length);
        splitMap[length] = calculatePossibleSplits(length);
    }
    return splitMap.at(length);
}

auto countRepeats(const std::vector<IDRange> &idRanges) {
    long doubles{};
    for (const auto &rng : idRanges) {
        // std::println("{}-{}", rng.leftRange, rng.rightRange);
        for (long i = rng.leftRange; i <= rng.rightRange; i++) {
            auto str_version = std::to_string(i);
            auto str_len = str_version.size();
            // std::print("Checking {}. Length: {} ", str_version, str_version.size());

            const std::vector<int> &numsToCheck = getPossibleSplits(str_len);
            // std::println("Possible splits: {}", numsToCheck);
            for (int checkNum : numsToCheck) {
                // std::print("Splitting in {}: ", checkNum);
                std::vector<std::string_view> splits(checkNum);
                for (auto toCheck : std::views::iota(0, checkNum)) {
                    auto window = str_len / checkNum;
                    splits[toCheck] = std::string_view(str_version).substr(toCheck * window, window);
                    // std::print("[{}]: {} /{} ", toCheck, splits[toCheck], window);
                }

                if (std::equal(splits.begin() + 1, splits.end(), splits.begin())) {
                    // std::print(" EQUAL!");
                    doubles += i;
                    break;
                }

                // std::println();
            }
            // std::println();
        }
        // std::println();
    }
    return doubles;
}

auto main() -> int {

    auto testCase = parseRanges("test_input");
    if (testCase) {
        auto testResult = countDoubles(*testCase);
        auto testResultP2 = countRepeats(*testCase);
        std::println("P1 Testcase result: {}", testResult);
        std::println("P2 Testcase result: {}", testResultP2);
    } else {
        std::print("{}\n", testCase.error());
    }

    auto realRanges = parseRanges("puzzle_input");
    if (realRanges) {
        // auto realResult = countDoubles(*realRanges);
        auto realResultP2 = countRepeats(*realRanges);
        // std::println("P1 Real result: {}", realResult);
        std::println("P2 Real result: {}", realResultP2);
    } else {
        std::print("{}\n", realRanges.error());
    }

    return 0;
}