Initial commit

2015/puzzle-18-02.cc

@@ -0,0 +1,111 @@
+#include <cassert>
+#include <cctype>
+#include <climits>
+#include <functional>
+#include <iostream>
+#include <map>
+#include <numeric>
+#include <regex>
+#include <set>
+#include <string>
+#include <variant>
+
+struct ConwayState {
+  ConwayState(std::size_t width, std::string const &s)
+      : width_(width), state_(width_ * width_, 0) {
+    assert(s.size() == width_ * width_);
+
+    flip(0);
+    flip(width_ - 1);
+    flip(width_ * (width_ - 1));
+    flip(width_ * width_ - 1);
+
+    for (std::size_t i = 0; i < state_.size(); ++i) {
+      if (s[i] == '#') {
+        flip(i);
+      }
+    }
+  }
+
+  ConwayState next_state() const {
+    ConwayState next(*this);
+    for (std::size_t i = 0; i < state_.size(); ++i) {
+      if (i == 0 || i == width_ - 1 || i == width_ * (width_ - 1) ||
+          i == width_ * width_ - 1) {
+        continue;
+      }
+      if (state_[i] == (2 | active_) || state_[i] == (3 | active_)) {
+        continue;
+      }
+      if (state_[i] == 3 || (state_[i] & active_) != 0) {
+        next.flip(i);
+      }
+    }
+
+    return next;
+  }
+
+  std::size_t num_active() const {
+    return std::accumulate(state_.begin(), state_.end(), std::size_t(0),
+                           [](std::size_t current, unsigned char info) {
+                             return current + ((info & active_) != 0);
+                           });
+  }
+
+private:
+  void flip(std::size_t idx) {
+    state_[idx] = state_[idx] ^ active_;
+    int delta = ((state_[idx] & active_) == active_) ? 1 : -1;
+    std::size_t row = idx / width_;
+    std::size_t col = idx % width_;
+    for (std::size_t r = std::max(std::size_t(1), row) - 1;
+         r < std::min(width_, row + 2); ++r) {
+      for (std::size_t c = std::max(std::size_t(1), col) - 1;
+           c < std::min(width_, col + 2); ++c) {
+        if (r == row && c == col) {
+          continue;
+        }
+        state_[r * width_ + c] = state_[r * width_ + c] + delta;
+      }
+    }
+  }
+
+  std::size_t width_;
+  std::vector<unsigned char> state_;
+
+  static constexpr unsigned char active_ = 0x80;
+  friend std::ostream &operator<<(std::ostream &os, ConwayState const &state);
+};
+
+std::ostream &operator<<(std::ostream &os, ConwayState const &state) {
+  std::size_t c = 0;
+  for (auto s : state.state_) {
+    os << (s & ConwayState::active_ ? '#' : '.');
+    os << (s & ~ConwayState::active_);
+    ++c;
+    if (c == state.width_) {
+      os << '\n';
+      c = 0;
+    }
+  }
+  return os;
+}
+
+int main(int argc, char **argv) {
+  std::string line;
+  std::size_t width = 0;
+  std::string init;
+  while (std::getline(std::cin, line)) {
+    if (width == 0) {
+      width = line.size();
+    }
+    assert(width == line.size());
+    init += line;
+  }
+  ConwayState conway(width, init);
+  for (unsigned i = 0; i < 100; ++i) {
+    conway = conway.next_state();
+  }
+  std::cout << "Solution: " << conway.num_active() << "\n";
+  return 0;
+}