From 56e890cec0a28c0a485212ccebfaf774235a79a2 Mon Sep 17 00:00:00 2001
From: Thomas Schmucker <ts@its1.de>
Date: Wed, 3 Jan 2024 23:35:54 +0100
Subject: prepare for more puzzles ... :)

---
 2023/src/day12.cpp | 182 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 182 insertions(+)
 create mode 100644 2023/src/day12.cpp

(limited to '2023/src/day12.cpp')

diff --git a/2023/src/day12.cpp b/2023/src/day12.cpp
new file mode 100644
index 0000000..11bd80b
--- /dev/null
+++ b/2023/src/day12.cpp
@@ -0,0 +1,182 @@
+#include <fstream>
+#include <iostream>
+#include <map>
+#include <sstream>
+#include <string>
+#include <vector>
+using namespace std;
+
+vector<string>
+read_file(string_view filename)
+{
+	fstream        input{ filename };
+	vector<string> data;
+
+	for ( string line; getline(input, line); ) {
+		data.emplace_back(line);
+	}
+
+	return data;
+}
+
+vector<string>
+split(const string& line, char sep)
+{
+	vector<string> parts{};
+	stringstream   input{ line };
+
+	for ( string part; getline(input, part, sep); ) {
+		parts.emplace_back(part);
+	}
+
+	return parts;
+}
+
+template<typename T = long>
+vector<T>
+read_ints(const string& line)
+{
+	vector<T>    parts{};
+	stringstream input{ line };
+
+	for ( string part; getline(input, part, ','); ) {
+		parts.emplace_back(stol(part));
+	}
+
+	return parts;
+}
+
+vector<long>
+count_groups(string_view str)
+{
+	vector<long> groups;
+
+	size_t idx = 0U;
+	while ( idx != str.length() ) {
+		while ( idx != str.length() && str[idx] == '.' ) {
+			++idx;
+		}
+		if ( idx != str.length() && str[idx] == '#' ) {
+			auto num = 0L;
+			while ( idx != str.length() && str[idx] == '#' ) {
+				++num;
+				++idx;
+			}
+			groups.emplace_back(num);
+		}
+	}
+
+	return groups;
+}
+
+long
+brute_force(string_view springs, const vector<long>& groups)
+{
+	long counts = count_if(springs.begin(), springs.end(), [](char chr) { return chr == '?'; });
+
+	string test_pattern;
+
+	auto arrangements = 0L;
+	for ( size_t counter = 0; counter != (1U << size_t(counts)); ++counter ) {
+		auto bit_pattern = counter;
+
+		for ( char chr: springs ) {
+			if ( chr == '?' ) {
+				if ( (bit_pattern & 1U) != 0U ) {
+					test_pattern += '.';
+				}
+				else {
+					test_pattern += '#';
+				}
+				bit_pattern >>= 1U;
+			}
+			else {
+				test_pattern += chr;
+			}
+		}
+		if ( groups == count_groups(test_pattern) ) {
+			arrangements++;
+		}
+
+		test_pattern.clear();
+	}
+
+	return arrangements;
+}
+
+long
+count(const string& springs, const vector<long>& groups)
+{
+	map<tuple<string, vector<long>>, long> cache;
+
+	function<long(string, const vector<long>&)> count_rec = [&](string springs, const vector<long>& groups) -> long {
+		auto cached_value = cache.find(make_tuple(springs, groups));
+		if ( cached_value != cache.end() ) {
+			return cached_value->second;
+		}
+
+		springs.erase(0, springs.find_first_not_of('.'));
+
+		if ( springs.empty() ) {
+			return groups.empty() ? 1 : 0;
+		}
+
+		if ( groups.empty() ) {
+			return springs.find('#') == string_view::npos ? 1 : 0;
+		}
+
+		if ( springs[0] == '#' ) {
+			auto gidx = size_t(groups[0]);
+			if ( springs.length() < gidx || springs.substr(0, gidx).find('.') != string_view::npos || springs[gidx] == '#' ) {
+				return 0;
+			}
+
+			return count_rec(springs.substr(gidx + 1), { groups.begin() + 1, groups.end() });
+		}
+
+		auto value = count_rec(string("#") + springs.substr(1), groups) + count_rec(springs.substr(1), groups);
+
+		cache[make_tuple(springs, groups)] = value;
+
+		return value;
+	};
+
+	return count_rec(springs + ".", groups);
+}
+
+void
+part1(const vector<string>& input)
+{
+	auto sum = 0L;
+	for ( const auto& line: input ) {
+		auto parts   = split(line, ' ');
+		auto springs = parts[0];
+		auto groups  = read_ints(parts[1]);
+
+		sum += brute_force(springs, groups);
+		// sum += count(springs, groups);
+	}
+	cout << sum << endl;
+}
+
+void
+part2(const vector<string>& input)
+{
+	auto sum = 0L;
+	for ( const auto& line: input ) {
+		auto parts   = split(line, ' ');
+		auto springs = parts[0] + "?" + parts[0] + "?" + parts[0] + "?" + parts[0] + "?" + parts[0];
+		auto groups  = read_ints(parts[1] + "," + parts[1] + "," + parts[1] + "," + parts[1] + "," + parts[1]);
+
+		sum += count(springs, groups);
+	}
+	cout << sum << endl;
+}
+
+int
+main()
+{
+	const auto input = read_file("data/day12.txt");
+	part1(input);
+	part2(input);
+}
-- 
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