Initial commit

2020/puzzle-24-01.cc

@@ -0,0 +1,64 @@
+#include <algorithm>
+#include <array>
+#include <cassert>
+#include <iostream>
+#include <list>
+#include <map>
+#include <regex>
+#include <set>
+#include <string>
+#include <tuple>
+#include <vector>
+
+using Coord = long;
+using Position = std::pair<Coord, Coord>;
+using Tiles = std::set<Position>;
+
+struct Tiler {
+  void flip_tile(std::string const &s) {
+    Coord x = 0;
+    Coord y = 0;
+    auto it = s.begin();
+    while (it != s.end()) {
+      Coord dx = 2;
+      if (*it == 's' || *it == 'n') {
+        y += (*it == 'n') - (*it == 's');
+        ++it;
+        dx = 1;
+        assert(it != s.end());
+      }
+
+      if (*it == 'e') {
+        x += dx;
+      } else if (*it == 'w') {
+        x -= dx;
+      } else {
+        assert(false);
+      }
+      ++it;
+    }
+
+    // Insert tile to be flipped - if we fail remove it.
+    auto [iit, success] = black_tiles_.insert({x, y});
+    if (!success) {
+      black_tiles_.erase(iit);
+    }
+  }
+
+  std::size_t black_count() const noexcept { return black_tiles_.size(); }
+
+private:
+  Tiles black_tiles_;
+};
+
+int main(void) {
+  Tiler tiler;
+  std::string line;
+  while (std::getline(std::cin, line)) {
+    tiler.flip_tile(line);
+  }
+
+  std::cout << "Number of black tiles: " << tiler.black_count() << "\n";
+
+  return 0;
+}