Clang tidy 2022 Day 9.

2022/puzzle-09-01.cc

@@ -0,0 +1,96 @@
+//
+// Created by Matthew Gretton-Dann on 09/12/2022.
+//
+
+#include <iostream>
+#include <numeric>
+#include <set>
+#include <string>
+#include <utility>
+
+using Int = std::int64_t;
+using Pos = std::pair<Int, Int>;
+
+struct compare_pos
+{
+  constexpr auto operator()(Pos const& l, Pos const& r) const noexcept
+  {
+    if (l.second < r.second) {
+      return true;
+    }
+    if (l.second == r.second && l.first < r.first) {
+      return true;
+    }
+    return false;
+  }
+};
+
+struct State
+{
+  State() { visited_.insert(tail_pos_);
+  }
+
+  auto move(Pos dir, Int steps)
+  {
+    for (Int i{0}; i != steps; ++i) {
+      head_pos_.first += dir.first;
+      head_pos_.second += dir.second;
+
+      if (std::abs(head_pos_.first - tail_pos_.first) > 1 ||
+          std::abs(head_pos_.second - tail_pos_.second) > 1) {
+        if (tail_pos_.first < head_pos_.first) {
+          ++tail_pos_.first;
+        }
+        if (tail_pos_.first > head_pos_.first) {
+          --tail_pos_.first;
+        }
+        if (tail_pos_.second < head_pos_.second) {
+          ++tail_pos_.second;
+        }
+        if (tail_pos_.second > head_pos_.second) {
+          --tail_pos_.second;
+        }
+        visited_.insert(tail_pos_);
+      }
+    }
+  }
+
+  [[nodiscard]] auto visited_count() const noexcept { return visited_.size(); }
+
+  Pos head_pos_{0, 0};
+  Pos tail_pos_{0, 0};
+  std::set<Pos, compare_pos> visited_;
+};
+
+auto main() -> int
+{
+  std::string line;
+  State state;
+
+  while (std::getline(std::cin, line) && !line.empty()) {
+    auto item{line[0]};
+    Pos dir{0, 0};
+    Int const amount{std::stoll(line.substr(2))};
+    switch (item) {
+    case 'L':
+      dir.first = -1;
+      break;
+    case 'R':
+      dir.first = 1;
+      break;
+    case 'U':
+      dir.second = 1;
+      break;
+    case 'D':
+      dir.second = -1;
+      break;
+    default:
+      std::cerr << "Unable to interpret: " << line << '\n';
+      return EXIT_FAILURE;
+    }
+    state.move(dir, amount);
+  }
+
+  std::cout << "Number of locations visited: " << state.visited_count() << '\n';
+  return 0;
+}