Day 8

src/days/08/Day08.cpp

@@ -1,9 +1,84 @@
 #include "Day08.h"
 
 Result Day08::Task1() {
-	return Day::Task1();
+	Map map = parseMap();
+	vector<uint8_t> instructions = parseInstructions();
+
+	uint64 steps = 0;
+	size_t instructionIndex = 0;
+	string node = "AAA";
+	while (node != "ZZZ"){
+		node = map[node][instructions[instructionIndex]];
+		steps++;
+		instructionIndex = (++instructionIndex) % instructions.size();
+	}
+
+	return to_string(steps);
 }
 
 Result Day08::Task2() {
-	return Day::Task2();
+	Map map = parseMap();
+	vector<uint8_t> instructions = parseInstructions();
+
+	vector<string> nodes;
+	for (auto [node, path] : map)
+		if (node.ends_with('A'))
+			nodes.push_back(node);
+
+	vector<uint64> allSteps;
+
+	for (string &node : nodes){
+		uint64 steps = 0;
+		size_t instructionIndex = 0;
+
+		while (!node.ends_with('Z')){
+			node = map[node][instructions[instructionIndex]];
+			steps++;
+			instructionIndex = (++instructionIndex) % instructions.size();
+		}
+
+		allSteps.push_back(steps);
+	}
+
+	uint64 lcm = 1;
+	for (uint64 steps : allSteps)
+		lcm = LCM(lcm, steps);
+
+	return to_string(lcm);
+}
+
+Day08::Map Day08::parseMap() const {
+	Map map;
+
+	for (size_t i = 2; i < input.size(); i++){
+		string line = input[i];
+		string source = line.substr(0, 3);
+		string left = line.substr(7, 3);
+		string right = line.substr(12, 3);
+		map[source] = {left, right};
+	}
+
+	return map;
+}
+
+vector<uint8_t> Day08::parseInstructions() const {
+	vector<uint8_t> instructions;
+
+	for (const char c : input[0])
+		instructions.push_back(c == 'L' ? 0 : 1);
+
+	return instructions;
+}
+
+uint64 Day08::GCD(uint64 a, uint64 b) {
+	while (b != 0){
+		uint64 t = b;
+		b = a % b;
+		a = t;
+	}
+	return a;
+}
+
+uint64 Day08::LCM(uint64 a, uint64 b) {
+	return a * b / GCD(a, b);
 }

src/days/08/Day08.h

@@ -3,8 +3,14 @@
 #include "../../Day.h"
 
 class Day08 : public Day {
+	typedef map<string, std::array<string, 2>> Map;
 protected:
 	Result Task1() override;
 
 	Result Task2() override;
+
+	vector<uint8_t> parseInstructions() const;
+	Map parseMap() const;
+	static uint64 GCD(uint64 a, uint64 b);
+	static uint64 LCM(uint64 a, uint64 b);
 };