aoc25/day2/main.cpp

#include <iostream>
#include <fstream>
#include <string>
#include <string_view>
#include <vector>
#include <expected>
#include <print>
#include <ranges>
#include <array>
#include <map>
#include <numeric>
#include <functional>
#include <algorithm>

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());

            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;
}