From 0febe907d18c670655756241cc319ce527ea3151 Mon Sep 17 00:00:00 2001
From: Matthew Gretton-Dann <matt@gretton-dann.org.uk>
Date: Tue, 12 Dec 2023 10:03:09 +0000
Subject: [PATCH] 2023 Day 12 Part 2 Proposed soln

Needs optimisation.
---
 2023/puzzle-12-02.cc | 132 +++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 132 insertions(+)
 create mode 100644 2023/puzzle-12-02.cc

diff --git a/2023/puzzle-12-02.cc b/2023/puzzle-12-02.cc
new file mode 100644
index 0000000..f43bc60
--- /dev/null
+++ b/2023/puzzle-12-02.cc
@@ -0,0 +1,132 @@
+#include <cstdint>
+#include <cstdlib>
+#include <iostream>
+#include <string>
+#include <string_view>
+#include <utility>
+#include <vector>
+
+using UInt = std::uint64_t;
+using StringVec = std::vector<std::string>;
+using UIntVec = std::vector<UInt>;
+using Pos = std::pair<UInt, UInt>;
+using PosVec = std::vector<Pos>;
+
+auto split(std::string_view line) -> std::pair<std::string_view, UIntVec>
+{
+  auto pos = line.find(' ');
+  auto pattern = line.substr(0, pos);
+  UIntVec nums;
+
+  line = line.substr(pos);
+  while (!line.empty()) {
+    line = line.substr(1);
+    char* n{nullptr};
+    nums.emplace_back(std::strtoll(line.data(), &n, 10));
+    line = line.substr(n - line.data());
+  }
+
+  return std::make_pair(pattern, nums);
+}
+
+[[nodiscard]] auto validate_subpattern(std::string_view pattern, std::string_view start,
+                                       UInt num_hashs, UInt gaps) -> bool
+{
+  if (pattern.size() < start.size()) {
+    return false;
+  }
+  UInt hash_count{0};
+
+  auto pit{pattern.begin()};
+  for (auto sit{start.begin()}; sit != start.end(); ++pit, ++sit) {
+    if (*sit == '#') { ++hash_count; }
+    if (*pit != '?' && *pit != *sit) {
+      return false;
+    }
+  }
+
+  for (; pit != pattern.end(); ++pit) {
+    if (*pit == '#') { ++hash_count; }
+  }
+
+  if (num_hashs < hash_count) {
+    return false;
+  }
+  if (start.size() + (num_hashs - hash_count) + gaps > pattern.size()) {
+    return false;
+  }
+
+  return true;
+}
+
+void generate_pattern(std::string start, UIntVec::const_iterator it, UIntVec::const_iterator end,
+                      std::string_view pattern, UInt hash_count, UInt& count)
+{
+  for (std::size_t p{0}; p + start.size() < pattern.size() && p < *it; ++p) {
+    if (pattern[start.size() + p] == '.') { return; }
+  }
+  start += std::string(*it++, '#');
+
+  if (it == end) {
+    if (start.size() <= pattern.size()) {
+      start.resize(pattern.size(), '.');
+      if (validate_subpattern(pattern, start, hash_count, end - it - 1)) {
+        ++count;
+        if (count % 100'000 == 0) {
+          std::cout << start << '\n';
+        }
+      }
+    }
+    return;
+  }
+
+  start += '.';
+  while (validate_subpattern(pattern, start, hash_count, end - it - 1)) {
+    generate_pattern(start, it, end, pattern, hash_count, count);
+    start += '.';
+  }
+}
+
+auto valid_sequences(std::string_view pattern, UIntVec const& nums) -> UInt
+{
+  UInt count{0};
+  UInt hash_count{0};
+  for (auto num : nums) { hash_count += num; }
+  std::string start;
+  while (validate_subpattern(pattern, start, hash_count, nums.size() - 1)) {
+    std::cout << start << '\n';
+    generate_pattern(start, nums.begin(), nums.end(), pattern, hash_count, count);
+    start += '.';
+  }
+
+  return count;
+}
+
+auto main() -> int try {
+  std::string line;
+  UInt count{0};
+
+  while (std::getline(std::cin, line)) {
+    auto [pattern, nums] = split(line);
+    UInt line_count{0};
+    std::string unfolded_pattern{pattern};
+    UIntVec unfolded_nums{nums.begin(), nums.end()};
+    for (unsigned i = 1; i < 5; ++i) {
+      unfolded_pattern += '?';
+      unfolded_pattern += pattern;
+      unfolded_nums.insert(unfolded_nums.begin(), nums.begin(), nums.end());
+    }
+
+    line_count += valid_sequences(unfolded_pattern, unfolded_nums);
+    std::cout << line << ": " << line_count << '\n';
+    count += line_count;
+  }
+
+  std::cout << "Valid sequences: " << count << '\n';
+
+  return EXIT_SUCCESS;;
+}
+catch (...) {
+  std::cerr << "Uncaught exception.\n";
+  return EXIT_FAILURE;
+}