Day15

src/days/15/Day15.cpp

@@ -1,19 +1,73 @@
 #include "Day15.h"
 
 Result Day15::Task1() {
-	Set sensors;
-	Set beacons;
+	int64 lowX = INT64_MAX, highX = INT64_MIN;
+	map<Point, uint64> sensorToBeaconDist;
+	Set sensors, beacons;
+	parseSystem(sensorToBeaconDist, sensors, beacons, lowX, highX);
+
+	int64 count = 0;
+	int64 y = 2000000;
+	for (int64 x = lowX; x <= highX; x++){
+		if (beacons.contains({x, y}))
+			continue;
+		for (const auto& pair : sensorToBeaconDist){
+			if (ManDist({x, y}, pair.first) <= pair.second){
+				count++;
+				break;
+			}
+		}
+	}
 
-	parseSystem(sensors, beacons);
 
-	return Day::Task1();
+	return to_string(count);
 }
 
 Result Day15::Task2() {
-	return Day::Task2();
+	int64 lowX = INT64_MAX, highX = INT64_MIN;
+	map<Point, uint64> sensorToBeaconDist;
+	Set sensors, beacons;
+	parseSystem(sensorToBeaconDist, sensors, beacons, lowX, highX);
+
+	const int64 low = 0;
+	const int64 high = 4000000;
+
+	for (const auto& pair : sensorToBeaconDist){
+		const Point sensor = pair.first;
+		const auto dist = int64(pair.second);
+
+		// Check all points touching the diamond, but not inside
+		for (int64 x = -dist - 1; x <= dist + 1; x++){
+			int64 yUp = dist + 1 - std::abs(x);
+			int64 yDown = -yUp;
+			int64 testX = x + sensor.first;
+			if (testX < low || testX > high)
+				continue;
+			int64 yArr[2] {yUp, yDown};
+			for (int64 &y : yArr){
+				int64 testY = y + sensor.second;
+				Point possibleSolution = {testX, testY};
+				if (testY < low || testY > high)
+					continue;
+				bool overlapped = false;
+				for (const auto& testPair : sensorToBeaconDist){
+					if (ManDist(possibleSolution, testPair.first) <= testPair.second){
+						overlapped = true;
+						break;
+					}
+				}
+				if (!overlapped){
+					int64 result = testX * 4000000 + testY;
+					return to_string(result);
+				}
+			}
+		}
+	}
+
+	return "Something went wrong";
 }
 
-void Day15::parseSystem(Set &sensors, Set &beacons) {
+void Day15::parseSystem(map<Point, uint64> &sensorToBeaconDist, Set &sensors, Set &beacons, int64& lowX, int64& highX) {
 	for (const string &line : input){
 		size_t xPos = line.find('x') + 2;
 		size_t yPos = line.find('y') + 2;
@@ -25,7 +79,17 @@ void Day15::parseSystem(Set &sensors, Set &beacons) {
 		int64 bx = stoi(line.substr(xPos, line.find(',', xPos) - xPos));
 		int64 by = stoi(line.substr(yPos));
 
+		uint64 dist = ManDist({sx, sy}, {bx, by});
+		int64 outerLeft = sx - int64(dist);
+		int64 outerRight = sx + int64(dist);
+		if (outerLeft < lowX) lowX = outerLeft;
+		if (outerRight > highX) highX = outerRight;
+		sensorToBeaconDist[{sx, sy}] = dist;
 		sensors.insert({sx, sy});
 		beacons.insert({bx, by});
 	}
 }
+
+uint64 Day15::ManDist(Day15::Point p1, Day15::Point p2) {
+	return std::abs(p2.first - p1.first) + std::abs(p2.second - p1.second);
+}

src/days/15/Day15.h

@@ -4,13 +4,14 @@
 
 class Day15 : public Day {
 	typedef pair<int64, int64> Point;
+	static uint64 ManDist(Point p1, Point p2);
 	struct hashFunction {
 		size_t operator()(const Point &p) const {
 			return p.first ^ p.second;
 		}
 	};
 	typedef unordered_set<Point, hashFunction> Set;
-	void parseSystem(Set&, Set&);
+	void parseSystem(map<Point, uint64>&, Set&, Set&, int64&, int64&);
 protected:
 	Result Task1() override;