Add 2016 day 7 puzzles

2016/puzzle-07-02.cc

@@ -0,0 +1,63 @@
+//
+// Created by Matthew Gretton-Dann on 04/12/2021.
+//
+
+#include <array>
+#include <iostream>
+#include <string>
+#include <vector>
+
+auto aba(std::string const& line) -> bool
+{
+  enum State { outside, inside };
+  using AbaArray = std::array<char, 2>;
+  std::vector<AbaArray> abas;
+  std::vector<AbaArray> pending_abas;
+
+  State state{outside};
+  for (std::size_t idx{0}; idx < line.size() - 2; ++idx) {
+    if (line[idx] == '[') {
+      state = inside;
+    }
+    else if (line[idx] == ']') {
+      state = outside;
+    }
+    else if (line[idx] != line[idx + 1] && line[idx] == line[idx + 2]) {
+      if (state == outside) {
+        char a{line[idx]};
+        char b{line[idx + 1]};
+        abas.push_back({a, b});
+        if (std::find_if(pending_abas.begin(), pending_abas.end(), [a, b](auto const& it) {
+              return it[0] == a && it[1] == b;
+            }) != pending_abas.end()) {
+          return true;
+        }
+      }
+      else {
+        char b{line[idx]};
+        char a{line[idx + 1]};
+        if (std::find_if(abas.begin(), abas.end(), [a, b](auto const& it) {
+              return it[0] == a && it[1] == b;
+            }) != abas.end()) {
+          return true;
+        }
+        pending_abas.push_back({a, b});
+      }
+    }
+  }
+
+  return false;
+}
+
+auto main() -> int
+{
+  std::string line;
+  unsigned good_count{0};
+  while (std::getline(std::cin, line)) {
+    if (aba(line)) {
+      ++good_count;
+    }
+  }
+  std::cout << "ABBA lines that support SSL: " << good_count << '\n';
+  return 0;
+}