72 lines
1.9 KiB
C++
72 lines
1.9 KiB
C++
//
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// Created by Matthew Gretton-Dann on 13/12/2021.
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//
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#include <iostream>
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#include <numeric>
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#include <regex>
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#include <set>
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#include <string>
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using Coord = std::pair<long, long>;
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using LightSet = std::set<Coord>;
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auto fold(LightSet const& lights, Coord const& fold_coord) -> LightSet
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{
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LightSet result;
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Coord shift{0, 0};
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for (auto const& c : lights) {
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Coord folded{c.first > fold_coord.first ? (2 * fold_coord.first - c.first) : c.first,
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c.second > fold_coord.second ? (2 * fold_coord.second - c.second) : c.second};
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shift = {std::min(shift.first, folded.first), std::min(shift.second, folded.second)};
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result.insert(folded);
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}
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if (shift == Coord{0, 0}) {
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return result;
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}
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LightSet result2;
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for (auto const& c : result) {
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result2.emplace(c.first - shift.first, c.second - shift.second);
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}
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return result2;
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}
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auto main() -> int
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{
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static std::regex fold_x{"fold along x=(\\d+)"};
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static std::regex fold_y{"fold along y=(\\d+)"};
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std::string line;
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LightSet lights;
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/* Read coords. */
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while (std::getline(std::cin, line) && !line.empty()) {
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std::size_t end{0};
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auto x{std::stol(line, &end)};
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auto y{std::stol(line.substr(end + 1))};
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lights.emplace(x, y);
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}
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/* Now do folds. */
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int count{0};
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std::cout << "Initial lights: " << lights.size() << '\n';
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while (std::getline(std::cin, line)) {
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std::smatch m;
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Coord fold_coord{std::numeric_limits<long>::max(), std::numeric_limits<long>::max()};
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if (std::regex_search(line, m, fold_x)) {
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fold_coord.first = std::stol(m.str(1));
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}
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else if (std::regex_search(line, m, fold_y)) {
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fold_coord.second = std::stol(m.str(1));
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}
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else {
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std::cerr << "Cannot interpret: " << line << "\n";
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return 1;
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}
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++count;
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lights = fold(lights, fold_coord);
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std::cout << "After " << count << " folds: " << lights.size() << '\n';
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}
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}
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