From d3999e2e8fd03c0592e9c132ef0559b019fedc25 Mon Sep 17 00:00:00 2001
From: Matthew Gretton-Dann <matt@gretton-dann.org.uk>
Date: Tue, 20 Dec 2022 21:31:31 +0000
Subject: [PATCH] Add solutions for 2018 day 5

---
 2018/puzzle-05-01.cc | 43 ++++++++++++++++++++++++++++++++++
 2018/puzzle-05-02.cc | 56 ++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 99 insertions(+)
 create mode 100644 2018/puzzle-05-01.cc
 create mode 100644 2018/puzzle-05-02.cc

diff --git a/2018/puzzle-05-01.cc b/2018/puzzle-05-01.cc
new file mode 100644
index 0000000..dfb4fd5
--- /dev/null
+++ b/2018/puzzle-05-01.cc
@@ -0,0 +1,43 @@
+//
+// Created by Matthew Gretton-Dann on 01/12/2022.
+//
+
+#include <cstdlib>
+#include <iomanip>
+#include <iostream>
+#include <map>
+#include <numeric>
+#include <set>
+#include <string>
+#include <utility>
+#include <vector>
+
+using UInt = std::uint64_t;
+
+using namespace std::string_literals;
+
+auto main() -> int
+{
+  std::string polymer;
+
+  if (!std::getline(std::cin, polymer)) {
+    std::cout << "Unable to read line.\n";
+    return EXIT_FAILURE;
+  }
+
+  auto it{polymer.begin()};
+  while ((it + 1) != polymer.end()) {
+    if (*it != *(it + 1) && (*it == std::tolower(*(it + 1)) || *it == std::toupper(*(it + 1)))) {
+      it = polymer.erase(it, it + 2);
+      if (it != polymer.begin()) {
+        --it;
+      }
+    }
+    else {
+      ++it;
+    }
+  }
+  std::cout << "Polymer: " << polymer << "\n";
+  std::cout << "Length: " << polymer.size() << "\n";
+  return EXIT_SUCCESS;
+}
diff --git a/2018/puzzle-05-02.cc b/2018/puzzle-05-02.cc
new file mode 100644
index 0000000..ce43f91
--- /dev/null
+++ b/2018/puzzle-05-02.cc
@@ -0,0 +1,56 @@
+//
+// Created by Matthew Gretton-Dann on 01/12/2022.
+//
+
+#include <algorithm>
+#include <cstdlib>
+#include <iomanip>
+#include <iostream>
+#include <numeric>
+#include <utility>
+
+using UInt = std::uint64_t;
+
+using namespace std::string_literals;
+
+auto amend_polymer(std::string polymer, char remove) -> std::string
+{
+  auto it{std::remove_if(polymer.begin(), polymer.end(),
+                         [remove](auto c) { return c == remove || (c == std::toupper(remove)); })};
+  return {polymer.begin(), it};
+}
+
+auto react_polymer(std::string polymer) -> UInt
+{
+  auto it{polymer.begin()};
+  while ((it + 1) != polymer.end()) {
+    if (*it != *(it + 1) && (*it == std::tolower(*(it + 1)) || *it == std::toupper(*(it + 1)))) {
+      it = polymer.erase(it, it + 2);
+      if (it != polymer.begin()) {
+        --it;
+      }
+    }
+    else {
+      ++it;
+    }
+  }
+  return polymer.size();
+}
+
+auto main() -> int
+{
+  std::string polymer;
+
+  if (!std::getline(std::cin, polymer)) {
+    std::cout << "Unable to read line.\n";
+    return EXIT_FAILURE;
+  }
+
+  UInt min_length{polymer.size() + 1};
+  for (char c{'a'}; c < 'z' + 1; ++c) {
+    std::string const poly2{amend_polymer(polymer, c)};
+    min_length = std::min(min_length, react_polymer(poly2));
+  }
+  std::cout << "Minimum length: " << min_length << "\n";
+  return EXIT_SUCCESS;
+}