Add 2016 day 18 puzzles

2016/puzzle-18-01.cc

@@ -0,0 +1,41 @@
+//
+// Created by Matthew Gretton-Dann on 07/12/2021.
+//
+
+#include <iostream>
+#include <numeric>
+#include <string>
+
+auto main() -> int
+{
+  std::string line;
+  if (!std::getline(std::cin, line)) {
+    std::cerr << "Unable to get line.\n";
+    return 1;
+  }
+
+  line = '.' + line + '.';
+  unsigned safe_count{0};
+  constexpr unsigned row_count{40};
+  for (unsigned row{0}; row < row_count; ++row) {
+    safe_count = std::accumulate(line.begin(), line.end(), safe_count,
+                                 [](unsigned a, char c) { return a + (c == '.' ? 1 : 0); }) -
+                 2;
+    std::string next_line{"."};
+    next_line.reserve(line.size());
+    for (unsigned i = 1; i < line.size() - 1; ++i) {
+      auto check{line.substr(i - 1, 3)};
+      if (check == "^^." || check == ".^^" || check == "^.." || check == "..^") {
+        next_line += '^';
+      }
+      else {
+        next_line += '.';
+      }
+    }
+    next_line += '.';
+    line = next_line;
+  }
+
+  std::cout << "Number of safe spots: " << safe_count << '\n';
+  return 0;
+}

2016/puzzle-18-02.cc

@@ -0,0 +1,41 @@
+//
+// Created by Matthew Gretton-Dann on 07/12/2021.
+//
+
+#include <iostream>
+#include <numeric>
+#include <string>
+
+auto main() -> int
+{
+  std::string line;
+  if (!std::getline(std::cin, line)) {
+    std::cerr << "Unable to get line.\n";
+    return 1;
+  }
+
+  line = '.' + line + '.';
+  unsigned safe_count{0};
+  constexpr unsigned row_count{400000};
+  for (unsigned row{0}; row < row_count; ++row) {
+    safe_count = std::accumulate(line.begin(), line.end(), safe_count,
+                                 [](unsigned a, char c) { return a + (c == '.' ? 1 : 0); }) -
+                 2;
+    std::string next_line{"."};
+    next_line.reserve(line.size());
+    for (unsigned i = 1; i < line.size() - 1; ++i) {
+      auto check{line.substr(i - 1, 3)};
+      if (check == "^^." || check == ".^^" || check == "^.." || check == "..^") {
+        next_line += '^';
+      }
+      else {
+        next_line += '.';
+      }
+    }
+    next_line += '.';
+    line = next_line;
+  }
+
+  std::cout << "Number of safe spots: " << safe_count << '\n';
+  return 0;
+}