From c6e9727f37409df0d774a49c0ed1496ab00cfad1 Mon Sep 17 00:00:00 2001
From: Matthew Gretton-Dann <matt@gretton-dann.org.uk>
Date: Sat, 9 Dec 2023 09:10:17 +0000
Subject: [PATCH] 2023 Day 9

---
 2023/puzzle-09-01.cc | 63 ++++++++++++++++++++++++++++++++++++++++++++
 2023/puzzle-09-02.cc | 63 ++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 126 insertions(+)
 create mode 100644 2023/puzzle-09-01.cc
 create mode 100644 2023/puzzle-09-02.cc

diff --git a/2023/puzzle-09-01.cc b/2023/puzzle-09-01.cc
new file mode 100644
index 0000000..8c66bd5
--- /dev/null
+++ b/2023/puzzle-09-01.cc
@@ -0,0 +1,63 @@
+#include <algorithm>
+#include <cstdint>
+#include <cstdlib>
+#include <iostream>
+#include <iterator>
+#include <stack>
+#include <string>
+#include <string_view>
+#include <vector>
+
+using Int = std::int64_t;
+using NumVec = std::vector<Int>;
+
+template<typename It>
+void read_nums(It it, std::string_view const nums)
+{
+  char const* pos{nums.data()};
+  while (pos - nums.data() < nums.size()) {
+    char* next_pos{nullptr};
+    *it++ = std::strtoll(pos, &next_pos, 10);
+    pos = next_pos;
+  }
+}
+
+constexpr auto is_zero(Int const num) -> bool { return num == 0; }
+
+auto main() -> int try {
+  std::string line;
+  Int sum{0};
+
+  while (std::getline(std::cin, line)) {
+    std::stack<NumVec> diffs;
+    diffs.emplace();
+    read_nums(std::back_inserter(diffs.top()), line);
+
+    while (!std::all_of(diffs.top().begin(), diffs.top().end(), is_zero)) {
+      NumVec diff;
+      auto const& top = diffs.top();
+      for (auto it = top.begin() + 1; it != top.end(); ++it) {
+        diff.emplace_back(*it - *(it - 1));
+      }
+      diffs.push(diff);
+    }
+
+    Int next{0};
+    while (!diffs.empty()) {
+      auto const& top = diffs.top();
+      next += top.back();
+      diffs.pop();
+    }
+
+    std::cout << line << ": " << next << '\n';
+    sum += next;
+  }
+
+  std::cout << "Sum: " << sum;
+
+  return EXIT_SUCCESS;
+}
+catch (...) {
+  std::cerr << "Uncaught exception.\n";
+  return EXIT_FAILURE;
+}
diff --git a/2023/puzzle-09-02.cc b/2023/puzzle-09-02.cc
new file mode 100644
index 0000000..34b48d5
--- /dev/null
+++ b/2023/puzzle-09-02.cc
@@ -0,0 +1,63 @@
+#include <algorithm>
+#include <cstdint>
+#include <cstdlib>
+#include <iostream>
+#include <iterator>
+#include <stack>
+#include <string>
+#include <string_view>
+#include <vector>
+
+using Int = std::int64_t;
+using NumVec = std::vector<Int>;
+
+template<typename It>
+void read_nums(It it, std::string_view const nums)
+{
+  char const* pos{nums.data()};
+  while (pos - nums.data() < nums.size()) {
+    char* next_pos{nullptr};
+    *it++ = std::strtoll(pos, &next_pos, 10);
+    pos = next_pos;
+  }
+}
+
+constexpr auto is_zero(Int const num) -> bool { return num == 0; }
+
+auto main() -> int try {
+  std::string line;
+  Int sum{0};
+
+  while (std::getline(std::cin, line)) {
+    std::stack<NumVec> diffs;
+    diffs.emplace();
+    read_nums(std::back_inserter(diffs.top()), line);
+
+    while (!std::all_of(diffs.top().begin(), diffs.top().end(), is_zero)) {
+      NumVec diff;
+      auto const& top = diffs.top();
+      for (auto it = top.begin() + 1; it != top.end(); ++it) {
+        diff.emplace_back(*it - *(it - 1));
+      }
+      diffs.push(diff);
+    }
+
+    Int next{0};
+    while (!diffs.empty()) {
+      auto const& top = diffs.top();
+      next = top.front() - next;
+      diffs.pop();
+    }
+
+    std::cout << line << ": " << next << '\n';
+    sum += next;
+  }
+
+  std::cout << "Sum: " << sum;
+
+  return EXIT_SUCCESS;
+}
+catch (...) {
+  std::cerr << "Uncaught exception.\n";
+  return EXIT_FAILURE;
+}