From be7eeaa5d32b3b65435713e08a84f1c4fb7514e7 Mon Sep 17 00:00:00 2001
From: Matthew Gretton-Dann <matt@gretton-dann.org.uk>
Date: Sun, 3 Dec 2023 09:40:50 +0000
Subject: [PATCH] 2023 Day 3 in a tidy form.

---
 2023/puzzle-03-01.cc | 78 ++++++++++++++++++++++++++++++++++++++
 2023/puzzle-03-02.cc | 89 ++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 167 insertions(+)
 create mode 100644 2023/puzzle-03-01.cc
 create mode 100644 2023/puzzle-03-02.cc

diff --git a/2023/puzzle-03-01.cc b/2023/puzzle-03-01.cc
new file mode 100644
index 0000000..ee3dff3
--- /dev/null
+++ b/2023/puzzle-03-01.cc
@@ -0,0 +1,78 @@
+#include <cassert>
+#include <cctype>
+#include <cstdint>
+#include <cstdlib>
+#include <iostream>
+#include <string>
+#include <vector>
+
+using UInt = std::uint64_t;
+
+constexpr auto is_digit_or_dot(char c) -> bool
+{
+  return (std::isdigit(c) != 0) || c == '.';
+}
+
+struct Grid
+{
+  void push(std::string const& s)
+  {
+    if (grid_.empty()) {
+      grid_.emplace_back(s.length() + 2, '.');
+      grid_.emplace_back(s.length() + 2, '.');
+    }
+
+    assert(s.length() + 2 == grid_.front().length());
+    grid_.emplace(grid_.end() - 1, std::string(".") + s + std::string("."));
+  }
+
+  [[nodiscard]] auto sum_parts() const -> UInt
+  {
+    UInt sum{0};
+    for (auto y{grid_.begin() + 1}; y != grid_.end(); ++y) {
+      for (auto x{y->begin() + 1}; x != y->end(); ++x) {
+        if (std::isdigit(*x) != 0) {
+          bool is_connected{false};
+          auto pos = x - y->begin();
+          UInt value = 0;
+          if (!is_digit_or_dot((y - 1)->at(pos - 1))) { is_connected = true; }
+          if (!is_digit_or_dot((y)->at(pos - 1))) { is_connected = true; }
+          if (!is_digit_or_dot((y + 1)->at(pos - 1))) { is_connected = true; }
+          while (std::isdigit(*x) != 0) {
+            value *= 10;
+            value += *x - '0';
+            if (!is_digit_or_dot((y - 1)->at(pos))) { is_connected = true; }
+            if (!is_digit_or_dot((y + 1)->at(pos))) { is_connected = true; }
+            ++x;
+            ++pos;
+          }
+          if (!is_digit_or_dot((y - 1)->at(pos))) { is_connected = true; }
+          if (!is_digit_or_dot((y)->at(pos))) { is_connected = true; }
+          if (!is_digit_or_dot((y + 1)->at(pos))) { is_connected = true; }
+          if (is_connected) { sum += value; }
+        }
+      }
+    }
+
+    return sum;
+  }
+
+  std::vector<std::string> grid_;
+};
+
+auto main() -> int try
+{
+  Grid grid;
+
+  std::string line;
+  while (std::getline(std::cin, line)) {
+    grid.push(line);
+  }
+
+  std::cout << "Part sum: " << grid.sum_parts() << '\n';
+  return EXIT_SUCCESS;
+}
+catch (...) {
+  std::cerr << "Uncaught exception.\n";
+  return EXIT_FAILURE;
+}
diff --git a/2023/puzzle-03-02.cc b/2023/puzzle-03-02.cc
new file mode 100644
index 0000000..696b0c0
--- /dev/null
+++ b/2023/puzzle-03-02.cc
@@ -0,0 +1,89 @@
+#include <cassert>
+#include <cctype>
+#include <cstdint>
+#include <cstdlib>
+#include <iostream>
+#include <map>
+#include <string>
+#include <utility>
+#include <vector>
+
+using UInt = std::uint64_t;
+
+struct Grid
+{
+  void push(std::string const& s)
+  {
+    if (grid_.empty()) {
+      grid_.emplace_back(s.length() + 2, '.');
+      grid_.emplace_back(s.length() + 2, '.');
+    }
+
+    assert(s.length() + 2 == grid_.front().length());
+    grid_.emplace(grid_.end() - 1, std::string(".") + s + std::string("."));
+  }
+
+  [[nodiscard]] auto loc(std::size_t const y, std::size_t const x) const -> UInt
+  {
+    return y * grid_.front().size() + x;
+  }
+
+  [[nodiscard]] auto sum_parts() const -> UInt
+  {
+    std::map<UInt, std::vector<UInt>> parts;
+
+    for (std::size_t y{1}; y < grid_.size(); ++y) {
+      for (auto x{1}; x < grid_[y].size(); ++x) {
+        if (std::isdigit(grid_[y][x]) != 0) {
+          std::vector<UInt> stars;
+          UInt value = 0;
+          if (grid_[y - 1][x - 1] == '*') { stars.emplace_back(loc(y - 1, x - 1)); }
+          if (grid_[y][x - 1] == '*') { stars.emplace_back(loc(y, x - 1)); }
+          if (grid_[y + 1][x - 1] == '*') { stars.emplace_back(loc(y + 1, x - 1)); }
+          while (std::isdigit(grid_[y][x]) != 0) {
+            value *= 10;
+            value += grid_[y][x] - '0';
+            if (grid_[y - 1][x] == '*') { stars.emplace_back(loc(y - 1, x)); }
+            if (grid_[y + 1][x] == '*') { stars.emplace_back(loc(y + 1, x)); }
+            ++x;
+          }
+          if (grid_[y - 1][x] == '*') { stars.emplace_back(loc(y - 1, x)); }
+          if (grid_[y][x] == '*') { stars.emplace_back(loc(y, x)); }
+          if (grid_[y + 1][x] == '*') { stars.emplace_back(loc(y + 1, x)); }
+
+          for (auto star : stars) {
+            auto [it, inserted] = parts.insert(std::make_pair(star, std::vector<UInt>()));
+            it->second.push_back(value);
+          }
+        }
+      }
+    }
+
+    UInt sum{0};
+    for (auto const& [id, sums] : parts) {
+      if (sums.size() == 2) {
+        sum += sums[0] * sums[1];
+      }
+    }
+
+    return sum;
+  }
+
+  std::vector<std::string> grid_;
+};
+
+auto main() -> int try {
+  Grid grid;
+
+  std::string line;
+  while (std::getline(std::cin, line)) {
+    grid.push(line);
+  }
+
+  std::cout << "Part sum: " << grid.sum_parts() << '\n';
+  return EXIT_SUCCESS;
+}
+catch (...) {
+  std::cerr << "Uncaught exception.\n";
+  return EXIT_FAILURE;
+}