diff --git a/AdventOfCode2024/PrintQueue.cpp b/AdventOfCode2024/PrintQueue.cpp index 65bdf9d..dee3eba 100644 --- a/AdventOfCode2024/PrintQueue.cpp +++ b/AdventOfCode2024/PrintQueue.cpp @@ -13,6 +13,7 @@ // You should have received a copy of the GNU General Public License along with // this program. If not, see . +#include #include #include @@ -77,7 +78,8 @@ void PrintQueue::processUpdatePages(const std::string& line) std::stringstream stream{ line }; std::string token; auto isCorrectOrder{ true }; - while (isCorrectOrder && std::getline(stream, token, ',')) + // We completely construct 'pages' for part 2, even if the ordering is not correct. + while (std::getline(stream, token, ',')) { size_t page = std::stoi(token); size_t i{ 0 }; @@ -86,14 +88,19 @@ void PrintQueue::processUpdatePages(const std::string& line) isCorrectOrder = !orderingRules_[page][pages[i]]; i++; } - if (isCorrectOrder) - { - pages.push_back(page); - } + pages.push_back(page); } if (isCorrectOrder) { part1 += pages[pages.size() / 2]; } + else + { + // This works because the input defines a complete ordering on the occurring + // page numbers. + std::sort(pages.begin(), pages.end(), + [&](int const& a, int const& b) { return orderingRules_[a][b]; }); + part2 += pages[pages.size() / 2]; + } } diff --git a/README.md b/README.md index c6fe225..a67202d 100644 --- a/README.md +++ b/README.md @@ -38,6 +38,12 @@ A simple [finite state machine](AdventOfCode2024/StringStateMachine.h) crawling For this puzzle I added a class for [points in two-dimensional space](AdventOfCode2024/Point2.h), so I can use these for simplifying directional computations. With that, the algorithm looks for all `X` and `A` for part 1 and 2, respectively, and tries to find the remaining characters, starting from that `X` or `A`. +### Day 5: Print Queue + +:mag_right: Puzzle: , :white_check_mark: Solver: [`PrintQueue.cpp`](AdventOfCode2024/PrintQueue.cpp) + +My implementation uses an ordering matrix (a two-dimensional boolean array) to track which page combinations are ordered, and then queries that matrix for each ordered combination of pages in a single line. The same matrix can then also be used for a custom sort function for part 2. + ## License Copyright (C) 2024 Stefan Müller