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solutions/day15/day15.go

@@ -0,0 +1,182 @@
+package day15
+
+import (
+	"bufio"
+	"fmt"
+	"os"
+	"strconv"
+)
+
+type Point struct {
+	x int
+	y int
+}
+
+func pointDistance(a Point, b Point) int {
+	return diff(a.x, b.x) + diff(a.y, b.y)
+}
+
+func diff(a int, b int) int {
+	if a > b {
+		return a - b
+	} else {
+		return b - a
+	}
+}
+
+type Sensor struct {
+	location Point
+	distance int
+}
+
+func parseLine(line string) (sensor Sensor, beacon Point) {
+	var sensorX int
+	var sensorY int
+	var beaconX int
+	var beaconY int
+
+	fmt.Sscanf(line, "Sensor at x=%d, y=%d: closest beacon is at x=%d, y=%d", &sensorX, &sensorY, &beaconX, &beaconY)
+	sensorLoc := Point{sensorX, sensorY}
+	beacon = Point{beaconX, beaconY}
+	distance := pointDistance(sensorLoc, beacon)
+	sensor = Sensor{sensorLoc, distance}
+	return
+}
+
+func isBeacon(x int, y int, beacons []Point) bool {
+	for _, beacon := range beacons {
+		if beacon.x == x && beacon.y == y {
+			return true
+		}
+	}
+	return false
+}
+
+func inSensorRange(x int, y int, sensors []Sensor) *Sensor {
+	point := Point{x, y}
+	for _, sensor := range sensors {
+		distance := pointDistance(point, sensor.location)
+		if distance <= sensor.distance {
+			return &sensor
+		}
+	}
+	return nil
+}
+
+func leftmostPoint(sensors []Sensor) int {
+	leftmost := 0
+
+	for _, sensor := range sensors {
+		candidate := sensor.location.x - sensor.distance
+		if candidate < leftmost {
+			leftmost = candidate
+		}
+	}
+
+	return leftmost
+}
+
+func rightmostPoint(sensors []Sensor) int {
+	rightmost := 0
+
+	for _, sensor := range sensors {
+		candidate := sensor.location.x + sensor.distance
+		if candidate > rightmost {
+			rightmost = candidate
+		}
+	}
+
+	return rightmost
+}
+
+func addLinePoints(pointSet *[]Point, start Point, end Point) {
+	offsetX := 1
+	offsetY := 1
+
+	if end.x < start.x {
+		offsetX = -1
+	}
+	if end.y < start.y {
+		offsetY = -1
+	}
+
+	for x, y := start.x, start.y; y != end.y; x, y = x+offsetX, y+offsetY {
+		*pointSet = append(*pointSet, Point{x, y})
+	}
+}
+
+func addEdgePoints(pointSet *[]Point, sensor Sensor) {
+	distance := sensor.distance + 1
+	top := Point{sensor.location.x, sensor.location.y - distance}
+	right := Point{sensor.location.x + distance, sensor.location.y}
+	bottom := Point{sensor.location.x, sensor.location.y + distance}
+	left := Point{sensor.location.x - distance, sensor.location.y}
+
+	addLinePoints(pointSet, top, right)
+	addLinePoints(pointSet, right, bottom)
+	addLinePoints(pointSet, bottom, left)
+	addLinePoints(pointSet, left, top)
+}
+
+func Run(filename string, yStr string, maxCoordStr string) {
+	y, err := strconv.Atoi(yStr)
+	if err != nil {
+		fmt.Println("PANIC: bad y argument", yStr)
+		return
+	}
+
+	maxCoord, err := strconv.Atoi(maxCoordStr)
+	if err != nil {
+		fmt.Println("PANIC: bad y argument", maxCoordStr)
+		return
+	}
+
+	file, err := os.Open(filename)
+
+	if err != nil {
+		fmt.Println("Error opening file:", err)
+		return
+	}
+
+	scanner := bufio.NewScanner(file)
+	scanner.Split(bufio.ScanLines)
+	sensors := []Sensor{}
+	beacons := []Point{}
+
+	for scanner.Scan() {
+		line := scanner.Text()
+		sensor, beacon := parseLine(line)
+		sensors = append(sensors, sensor)
+		beacons = append(beacons, beacon)
+	}
+
+	file.Close()
+
+	fmt.Println(sensors)
+
+	count := 0
+	for x := leftmostPoint(sensors); x <= rightmostPoint(sensors); x++ {
+		if isBeacon(x, y, beacons) {
+			continue
+		}
+
+		if inSensorRange(x, y, sensors) != nil {
+			count += 1
+		}
+	}
+	fmt.Println("Beacons couldn't be in", count, "places on line", y)
+
+	candidates := []Point{}
+	for _, sensor := range sensors {
+		addEdgePoints(&candidates, sensor)
+	}
+
+	for _, candidate := range candidates {
+		if candidate.x >= 0 && candidate.y >= 0 && candidate.x <= maxCoord && candidate.y <= maxCoord {
+			closestSensor := inSensorRange(candidate.x, candidate.y, sensors)
+			if closestSensor == nil {
+				fmt.Printf("Found possible beacon location at (%d, %d). Frequency value is %d\n", candidate.x, candidate.y, candidate.x*4000000+candidate.y)
+			}
+		}
+	}
+}