Initial commit

2020/puzzle-11-01.cc

@@ -0,0 +1,96 @@
+#include <algorithm>
+#include <array>
+#include <cassert>
+#include <iostream>
+#include <list>
+#include <map>
+#include <regex>
+#include <string>
+
+using Array = std::vector<std::string>;
+
+char next_state(Array const &a, std::size_t row, std::size_t col) {
+  unsigned occupied = 0;
+  if (row > 0) {
+    if (col > 0) {
+      occupied += (a[row - 1][col - 1] == '#');
+    }
+    occupied += a[row - 1][col] == '#';
+    if (col < a[row - 1].size() - 1) {
+      occupied += (a[row - 1][col + 1] == '#');
+    }
+  }
+  if (col > 0) {
+    occupied += (a[row][col - 1] == '#');
+  }
+  if (col < a[row].size() - 1) {
+    occupied += (a[row][col + 1] == '#');
+  }
+  if (row < a.size() - 1) {
+    if (col > 0) {
+      occupied += (a[row + 1][col - 1] == '#');
+    }
+    occupied += a[row + 1][col] == '#';
+    if (col < a[row + 1].size() - 1) {
+      occupied += (a[row + 1][col + 1] == '#');
+    }
+  }
+
+  if (a[row][col] == 'L' && occupied == 0) {
+    return '#';
+  } else if (a[row][col] == '#' && occupied >= 4) {
+    return 'L';
+  } else {
+    return a[row][col];
+  }
+}
+
+unsigned long count_occupied(Array const &a) {
+  unsigned long count = 0;
+  for (auto const &row : a) {
+    for (auto col : row) {
+      count += (col == '#');
+    }
+  }
+
+  return count;
+}
+
+unsigned long run_to_steady_state(Array const &a) {
+  Array current = a;
+  bool changed = true;
+  unsigned i = 0;
+  while (changed) {
+    std::cout << "------ iter = " << i++ << "\n";
+    changed = false;
+    Array next;
+    for (std::size_t row = 0; row < current.size(); ++row) {
+      std::string s = "";
+      for (std::size_t col = 0; col < current[row].size(); ++col) {
+        char c = next_state(current, row, col);
+        s.push_back(c);
+        if (c != current[row][col]) {
+          changed = true;
+        }
+      }
+      next.push_back(s);
+      std::cout << s << "\n";
+    }
+    current = next;
+  }
+
+  return count_occupied(current);
+}
+int main(int argc, char **argv) {
+  Array array;
+
+  for (std::string line; std::getline(std::cin, line);) {
+    array.push_back(line);
+    std::cout << line << "\n";
+  }
+
+  unsigned long result = run_to_steady_state(array);
+
+  std::cout << "Number of occupied states: " << result << "\n";
+  return 0;
+}