Add 2016 day 7 puzzles

2016/puzzle-07-01.cc

@@ -0,0 +1,40 @@
+//
+// Created by Matthew Gretton-Dann on 04/12/2021.
+//
+
+#include <array>
+#include <iostream>
+#include <string>
+
+auto abba(std::string const& line)
+{
+  enum State { outside, inside };
+  std::array<bool, 2> seen{false, false};
+  State state{State::outside};
+  for (std::size_t idx{0}; idx < line.size() - 3; ++idx) {
+    if (line[idx] == '[') {
+      state = State::inside;
+    }
+    else if (line[idx] == ']') {
+      state = State::outside;
+    }
+    else if (line[idx] != line[idx + 1] && line[idx + 1] == line[idx + 2] &&
+             line[idx] == line[idx + 3]) {
+      seen[static_cast<unsigned>(state)] = true;
+    }
+  }
+  return seen[State::outside] && !seen[State::inside];
+}
+
+auto main() -> int
+{
+  std::string line;
+  unsigned good_count{0};
+  while (std::getline(std::cin, line)) {
+    if (abba(line)) {
+      ++good_count;
+    }
+  }
+  std::cout << "ABBA lines that support TLS: " << good_count << '\n';
+  return 0;
+}