From 0a41c0529d27d2604f0ee23f49dcc076207738f6 Mon Sep 17 00:00:00 2001
From: Matthew Gretton-Dann <matt@gretton-dann.org.uk>
Date: Fri, 15 Dec 2023 08:48:52 +0000
Subject: [PATCH] 2023 Day 15

---
 2023/puzzle-15-01.cc | 45 +++++++++++++++++++++++++
 2023/puzzle-15-02.cc | 79 ++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 124 insertions(+)
 create mode 100644 2023/puzzle-15-01.cc
 create mode 100644 2023/puzzle-15-02.cc

diff --git a/2023/puzzle-15-01.cc b/2023/puzzle-15-01.cc
new file mode 100644
index 0000000..9bfba73
--- /dev/null
+++ b/2023/puzzle-15-01.cc
@@ -0,0 +1,45 @@
+#include <cstdint>
+#include <cstdlib>
+#include <iostream>
+#include <string>
+#include <string_view>
+
+using UInt = std::uint64_t;
+
+auto hash(std::string_view const str) -> std::uint8_t
+{
+  std::uint8_t hash{0};
+  for (auto const c : str) {
+    hash += static_cast<std::uint8_t>(c);
+    hash += hash << 4;
+  }
+
+  return hash;
+}
+
+auto main() -> int try {
+  std::string line;
+  UInt total_hash{0};
+
+  if (!std::getline(std::cin, line)) {
+    std::cerr << "Unable to read input.";
+  }
+
+  std::size_t pos{0};
+  while (pos < line.size()) {
+    auto next_pos = line.find(',', pos);
+    if (next_pos == std::string::npos) { next_pos = line.size(); }
+    auto const h = hash(line.substr(pos, next_pos - pos));
+    std::cout << line.substr(pos, next_pos - pos) << ": " << static_cast<unsigned>(h) << '\n';
+    total_hash += h;
+    pos = next_pos + 1;
+  }
+
+  std::cout << "Total: " << total_hash << '\n';
+
+  return EXIT_SUCCESS;
+}
+catch (...) {
+  std::cerr << "Uncaught exception.\n";
+  return EXIT_FAILURE;
+}
diff --git a/2023/puzzle-15-02.cc b/2023/puzzle-15-02.cc
new file mode 100644
index 0000000..97c8dc8
--- /dev/null
+++ b/2023/puzzle-15-02.cc
@@ -0,0 +1,79 @@
+#include <algorithm>
+#include <cstddef>
+#include <cstdint>
+#include <cstdlib>
+#include <iostream>
+#include <list>
+#include <string>
+#include <string_view>
+#include <utility>
+#include <vector>
+
+using UInt = std::uint64_t;
+using Lens = std::pair<std::string_view, UInt>;
+using LensList = std::list<Lens>;
+
+auto hash(std::string_view const str) -> std::uint8_t
+{
+  std::uint8_t hash{0};
+  for (auto const c : str) {
+    hash += static_cast<std::uint8_t>(c);
+    hash += hash << 4;
+  }
+
+  return hash;
+}
+
+auto main() -> int try {
+  std::string line;
+  std::vector<LensList> lenses(256);
+
+  if (!std::getline(std::cin, line)) {
+    std::cerr << "Unable to read input.";
+  }
+
+  for (std::ptrdiff_t pos{0}; pos < line.size(); ++pos) {
+    auto const start{pos};
+    while (line[pos] != '-' && line[pos] != '=') { ++pos; }
+    std::string_view const id{line.begin() + start, line.begin() + pos};
+    auto const h = hash(id);
+    auto& box = lenses[h];
+    auto it = std::ranges::find_if(box, [id](Lens const& l) {
+      return l.first == id;
+    });
+    if (line[pos] == '-') {
+      if (it != box.end()) {
+        box.erase(it);
+      }
+      ++pos;
+    }
+    else if (line[pos] == '=') {
+      if (it != box.end()) {
+        it->second = line[pos + 1] - '0';
+      }
+      else {
+        box.emplace_back(id, line[pos + 1] - '0');
+      }
+      pos += 2;
+    }
+    else { std::abort(); }
+  }
+
+  UInt total{0};
+  UInt box_id{1};
+  for (auto const& box : lenses) {
+    UInt lens_id{1};
+    for (auto const [id, focal_length] : box) {
+      total += box_id * lens_id * focal_length;
+      ++lens_id;
+    }
+    ++box_id;
+  }
+  std::cout << "Total: " << total << '\n';
+
+  return EXIT_SUCCESS;
+}
+catch (...) {
+  std::cerr << "Uncaught exception.\n";
+  return EXIT_FAILURE;
+}