From f52cf2888ddc30c4dc181b88d2a7077ac36f098f Mon Sep 17 00:00:00 2001
From: Thomas Schmucker <ts@its1.de>
Date: Tue, 19 Nov 2024 20:44:58 +0100
Subject: aoc 2015, day 19

---
 2015/src/day19.cpp | 115 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 115 insertions(+)
 create mode 100644 2015/src/day19.cpp

diff --git a/2015/src/day19.cpp b/2015/src/day19.cpp
new file mode 100644
index 0000000..7801964
--- /dev/null
+++ b/2015/src/day19.cpp
@@ -0,0 +1,115 @@
+#include <algorithm>
+#include <cstddef>
+#include <fstream>
+#include <iostream>
+#include <map>
+#include <set>
+#include <sstream>
+#include <string>
+#include <tuple>
+#include <vector>
+using namespace std;
+
+auto
+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;
+}
+
+tuple<string, vector<tuple<string, string>>>
+read_file(string_view filename)
+{
+	fstream                       input{ filename };
+	vector<tuple<string, string>> table;
+	string                        molecule;
+
+	for ( string line; getline(input, line); ) {
+		auto parts = split(line);
+
+		if ( parts.size() == 3 && parts[1] == "=>" ) {
+			table.emplace_back(parts[0], parts[2]);
+		}
+
+		if ( parts.size() == 1 ) {
+			molecule = parts[0];
+		}
+	}
+	return { molecule, table };
+}
+
+void
+part1(const string& molecule, const vector<tuple<string, string>>& table)
+{
+	set<string> set;
+	for ( const auto& [left, right]: table ) {
+		size_t pos = 0;
+		while ( true ) {
+			string temp = molecule;
+			pos         = temp.find(left, pos);
+			if ( pos == string::npos ) {
+				break;
+			}
+			temp.replace(pos, left.length(), right);
+			++pos;
+
+			set.insert(temp);
+		}
+	}
+	cout << set.size() << endl;
+}
+
+size_t
+replace_all(string& str, string_view replace, string_view replaceWith)
+{
+	size_t count = 0;
+	auto   pos   = str.find(replace);
+
+	while ( pos != string::npos ) {
+		str.replace(pos, replace.size(), replaceWith);
+		++count;
+		pos = str.find(replace, pos + replace.size());
+	}
+
+	return count;
+}
+
+void
+part2(string molecule)
+{
+	replace_all(molecule, "Rn", "(");
+	replace_all(molecule, "Y", ",");
+	replace_all(molecule, "Ar", ")");
+
+	molecule.erase(remove_if(molecule.begin(), molecule.end(), [](auto chr) -> bool {
+		               return islower(chr);
+	               }),
+	               molecule.end());
+
+	transform(molecule.begin(), molecule.end(), molecule.begin(), [](auto chr) {
+		return isalpha(chr) ? 'X' : chr;
+	});
+
+	size_t count = 0;
+	while ( molecule != "X" ) {
+		for ( const auto& item: { "XX", "X(X)", "X(X,X)", "X(X,X,X)" } ) {
+			count += replace_all(molecule, item, "X");
+		}
+	}
+
+	cout << count << endl;
+}
+
+int
+main()
+{
+	const auto [molecule, table] = read_file("data/day19.txt");
+	part1(molecule, table);
+	part2(molecule);
+}
-- 
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