From 43394ea57b4f492b51e8d3492ffe841f1bc0ecc6 Mon Sep 17 00:00:00 2001
From: Thomas Schmucker <ts@its1.de>
Date: Mon, 6 Jan 2025 11:10:14 +0100
Subject: aoc 2015, day 23

---
 2015/src/day23.cpp | 144 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 144 insertions(+)
 create mode 100644 2015/src/day23.cpp

diff --git a/2015/src/day23.cpp b/2015/src/day23.cpp
new file mode 100644
index 0000000..80281da
--- /dev/null
+++ b/2015/src/day23.cpp
@@ -0,0 +1,144 @@
+#include <fstream>
+#include <iostream>
+#include <string>
+#include <tuple>
+#include <vector>
+using namespace std;
+
+enum Instruction {
+	Half_A,
+	Half_B,
+	Triple_A,
+	Triple_B,
+	Inc_A,
+	Inc_B,
+	Jmp,
+	Jmp_Even_A,
+	Jmp_Even_B,
+	Jmp_One_A,
+	Jmp_One_B
+};
+
+vector<tuple<Instruction, int>>
+read_file(string_view filename)
+{
+	fstream input{ filename };
+
+	vector<tuple<Instruction, int>> instructions;
+	for ( string line; getline(input, line); ) {
+		if ( line == "hlf a" ) {
+			instructions.emplace_back(Half_A, 0);
+		}
+		else if ( line == "hlf b" ) {
+			instructions.emplace_back(Half_B, 0);
+		}
+		else if ( line == "tpl a" ) {
+			instructions.emplace_back(Triple_A, 0);
+		}
+		else if ( line == "tpl b" ) {
+			instructions.emplace_back(Triple_B, 0);
+		}
+		else if ( line == "inc a" ) {
+			instructions.emplace_back(Inc_A, 0);
+		}
+		else if ( line == "inc b" ) {
+			instructions.emplace_back(Inc_B, 0);
+		}
+		else if ( line.starts_with("jmp ") ) {
+			auto offset = stoi(line.substr(4));
+			instructions.emplace_back(Jmp, offset);
+		}
+		else if ( line.starts_with("jie a, ") ) {
+			auto offset = stoi(line.substr(7));
+			instructions.emplace_back(Jmp_Even_A, offset);
+		}
+		else if ( line.starts_with("jie b, ") ) {
+			auto offset = stoi(line.substr(7));
+			instructions.emplace_back(Jmp_Even_B, offset);
+		}
+		else if ( line.starts_with("jio a, ") ) {
+			auto offset = stoi(line.substr(7));
+			instructions.emplace_back(Jmp_One_A, offset);
+		}
+		else if ( line.starts_with("jio b, ") ) {
+			auto offset = stoi(line.substr(7));
+			instructions.emplace_back(Jmp_One_B, offset);
+		}
+		else {
+			cerr << "unknown instruction: " << line << endl;
+		}
+	}
+	return instructions;
+}
+
+int
+eval(const vector<tuple<Instruction, int>>& instructions, int a, int b)
+{
+	for ( size_t ip = 0; ip < instructions.size(); ) {
+		const auto [instruction, offset] = instructions[ip++];
+		switch ( instruction ) {
+		case Half_A:
+			a /= 2;
+			break;
+		case Half_B:
+			b /= 2;
+			break;
+		case Triple_A:
+			a *= 3;
+			break;
+		case Triple_B:
+			b *= 3;
+			break;
+		case Inc_A:
+			a++;
+			break;
+		case Inc_B:
+			b++;
+			break;
+		case Jmp:
+			ip = (ip - 1) + size_t(offset);
+			break;
+		case Jmp_Even_A:
+			if ( a % 2 == 0 ) {
+				ip = (ip - 1) + size_t(offset);
+			}
+			break;
+		case Jmp_Even_B:
+			if ( b % 2 == 0 ) {
+				ip = (ip - 1) + size_t(offset);
+			}
+			break;
+		case Jmp_One_A:
+			if ( a == 1 ) {
+				ip = (ip - 1) + size_t(offset);
+			}
+			break;
+		case Jmp_One_B:
+			if ( b == 1 ) {
+				ip = (ip - 1) + size_t(offset);
+			}
+			break;
+		}
+	}
+	return b;
+}
+
+void
+part1(const vector<tuple<Instruction, int>>& instructions)
+{
+	cout << eval(instructions, 0, 0) << endl;
+}
+
+void
+part2(const vector<tuple<Instruction, int>>& instructions)
+{
+	cout << eval(instructions, 1, 0) << endl;
+}
+
+int
+main()
+{
+	auto instructions = read_file("data/day23.txt");
+	part1(instructions);
+	part2(instructions);
+}
-- 
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