Solutions for 2018 day 10

2018/puzzle-10-01.cc

@@ -0,0 +1,99 @@
+//
+// Created by Matthew Gretton-Dann on 01/12/2022.
+//
+
+#include <algorithm>
+#include <cstdlib>
+#include <iomanip>
+#include <iostream>
+#include <map>
+#include <regex>
+#include <utility>
+
+using Int = std::int64_t;
+using Point = std::pair<Int, Int>;
+
+struct Star
+{
+  auto time_step() noexcept
+  {
+    pos_.first += velocity_.first;
+    pos_.second += velocity_.second;
+  }
+  Point pos_;
+  Point velocity_;
+};
+
+using Stars = std::vector<Star>;
+
+auto vert_dist(Stars const& stars)
+{
+  auto [min, max] =
+    std::minmax_element(stars.begin(), stars.end(),
+                        [](auto const& l, auto const& r) { return l.pos_.second < r.pos_.second; });
+  return max->pos_.second - min->pos_.second;
+}
+
+auto main() -> int
+{
+  std::string line;
+  std::regex const re{R"(position=<\s*(-?\d+),\s*(-?\d+)> velocity=<\s*(-?\d+),\s*(-?\d+)>)"};
+
+  Stars stars;
+  while (std::getline(std::cin, line)) {
+    std::smatch m;
+    if (!std::regex_match(line, m, re)) {
+      std::cerr << "Unable to interpret: " << line << "\n";
+      return EXIT_FAILURE;
+    }
+
+    Star star;
+    star.pos_.first = std::stoll(m.str(1));
+    star.pos_.second = std::stoll(m.str(2));
+    star.velocity_.first = std::stoll(m.str(3));
+    star.velocity_.second = std::stoll(m.str(4));
+    stars.push_back(star);
+  }
+
+  auto range{vert_dist(stars)};
+  auto old_range{range + 1};
+  Stars old_stars;
+  Int time{-1};
+
+  // We continue until the vertical range starts getting bigger.
+  while (range < old_range) {
+    old_range = range;
+    old_stars = stars;
+    for (auto& star : stars) {
+      star.time_step();
+    }
+    range = vert_dist(stars);
+    ++time;
+  }
+
+  // We want to use the smallest star set.
+  stars = old_stars;
+  auto [min_x_elt, max_x_elt] =
+    std::minmax_element(stars.begin(), stars.end(),
+                        [](auto const& l, auto const& r) { return l.pos_.first < r.pos_.first; });
+  auto [min_y_elt, max_y_elt] =
+    std::minmax_element(stars.begin(), stars.end(),
+                        [](auto const& l, auto const& r) { return l.pos_.second < r.pos_.second; });
+  auto min_x{min_x_elt->pos_.first};
+  auto max_x{max_x_elt->pos_.first};
+  auto min_y{min_y_elt->pos_.second};
+  auto max_y{max_y_elt->pos_.second};
+  std::vector<std::string> strings(max_y - min_y + 1);
+  for (auto& s : strings) {
+    s.resize(max_x - min_x + 1, ' ');
+  }
+  for (auto const& star : stars) {
+    strings.at(star.pos_.second - min_y).at(star.pos_.first - min_x) = '#';
+  }
+  for (auto const& s : strings) {
+    std::cout << s << "\n";
+  }
+  std::cout <<"In " << time << " seconds.\n";
+
+  return EXIT_SUCCESS;
+}

2018/puzzle-10-02.cc

@@ -0,0 +1,99 @@
+//
+// Created by Matthew Gretton-Dann on 01/12/2022.
+//
+
+#include <algorithm>
+#include <cstdlib>
+#include <iomanip>
+#include <iostream>
+#include <map>
+#include <regex>
+#include <utility>
+
+using Int = std::int64_t;
+using Point = std::pair<Int, Int>;
+
+struct Star
+{
+  auto time_step() noexcept
+  {
+    pos_.first += velocity_.first;
+    pos_.second += velocity_.second;
+  }
+  Point pos_;
+  Point velocity_;
+};
+
+using Stars = std::vector<Star>;
+
+auto vert_dist(Stars const& stars)
+{
+  auto [min, max] =
+    std::minmax_element(stars.begin(), stars.end(),
+                        [](auto const& l, auto const& r) { return l.pos_.second < r.pos_.second; });
+  return max->pos_.second - min->pos_.second;
+}
+
+auto main() -> int
+{
+  std::string line;
+  std::regex const re{R"(position=<\s*(-?\d+),\s*(-?\d+)> velocity=<\s*(-?\d+),\s*(-?\d+)>)"};
+
+  Stars stars;
+  while (std::getline(std::cin, line)) {
+    std::smatch m;
+    if (!std::regex_match(line, m, re)) {
+      std::cerr << "Unable to interpret: " << line << "\n";
+      return EXIT_FAILURE;
+    }
+
+    Star star;
+    star.pos_.first = std::stoll(m.str(1));
+    star.pos_.second = std::stoll(m.str(2));
+    star.velocity_.first = std::stoll(m.str(3));
+    star.velocity_.second = std::stoll(m.str(4));
+    stars.push_back(star);
+  }
+
+  auto range{vert_dist(stars)};
+  auto old_range{range + 1};
+  Stars old_stars;
+  Int time{-1};
+
+  // We continue until the vertical range starts getting bigger.
+  while (range < old_range) {
+    old_range = range;
+    old_stars = stars;
+    for (auto& star : stars) {
+      star.time_step();
+    }
+    range = vert_dist(stars);
+    ++time;
+  }
+
+  // We want to use the smallest star set.
+  stars = old_stars;
+  auto [min_x_elt, max_x_elt] =
+    std::minmax_element(stars.begin(), stars.end(),
+                        [](auto const& l, auto const& r) { return l.pos_.first < r.pos_.first; });
+  auto [min_y_elt, max_y_elt] =
+    std::minmax_element(stars.begin(), stars.end(),
+                        [](auto const& l, auto const& r) { return l.pos_.second < r.pos_.second; });
+  auto min_x{min_x_elt->pos_.first};
+  auto max_x{max_x_elt->pos_.first};
+  auto min_y{min_y_elt->pos_.second};
+  auto max_y{max_y_elt->pos_.second};
+  std::vector<std::string> strings(max_y - min_y + 1);
+  for (auto& s : strings) {
+    s.resize(max_x - min_x + 1, ' ');
+  }
+  for (auto const& star : stars) {
+    strings.at(star.pos_.second - min_y).at(star.pos_.first - min_x) = '#';
+  }
+  for (auto const& s : strings) {
+    std::cout << s << "\n";
+  }
+  std::cout <<"In " << time << " seconds.\n";
+
+  return EXIT_SUCCESS;
+}