d5

d5/d5.go

@@ -0,0 +1,88 @@
+package d5
+
+import (
+	"math"
+	"strconv"
+	"strings"
+)
+
+type point struct {
+	x int
+	y int
+}
+
+type segment struct {
+	a point
+	b point
+}
+
+func createSegments(lines []string) []segment {
+	segments := make([]segment, len(lines))
+	for i, line := range lines {
+		points := strings.Split(line, " -> ")
+		start := strings.Split(points[0], ",")
+		end := strings.Split(points[1], ",")
+		x1, _ := strconv.Atoi(start[0])
+		y1, _ := strconv.Atoi(start[1])
+		x2, _ := strconv.Atoi(end[0])
+		y2, _ := strconv.Atoi(end[1])
+		segments[i] = segment{point{x1, y1}, point{x2, y2}}
+	}
+
+	return segments
+}
+
+func generatePoints(segments []segment) []point {
+	points := []point{}
+
+	for _, segment := range segments {
+		if segment.a.x == segment.b.x {
+			min := int(math.Min(float64(segment.a.y), float64(segment.b.y)))
+			max := int(math.Max(float64(segment.a.y), float64(segment.b.y)))
+			for i := min; i <= max; i++ {
+				points = append(points, point{segment.a.x, i})
+			}
+		}
+
+		if segment.a.y == segment.b.y {
+			min := int(math.Min(float64(segment.a.x), float64(segment.b.x)))
+			max := int(math.Max(float64(segment.a.x), float64(segment.b.x)))
+			for i := min; i <= max; i++ {
+				points = append(points, point{i, segment.a.y})
+			}
+		}
+	}
+
+	return points
+}
+
+func findIntersections(points []point) map[point]int {
+
+	intersections := map[point]int{}
+
+	for _, a := range points {
+		intersections[a]++
+	}
+
+	return intersections
+}
+
+func countIntersections(intersections map[point]int) int {
+	count := 0
+
+	for _, crosses := range intersections {
+		if crosses > 1 {
+			count++
+		}
+	}
+
+	return count
+}
+
+func D5(input string) int {
+	lines := strings.Split(strings.TrimSpace(input), "\n")
+	segments := createSegments(lines)
+	points := generatePoints(segments)
+	intersections := findIntersections(points)
+	return countIntersections(intersections)
+}

d5/d5_test.go

@@ -0,0 +1,22 @@
+package d5
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestD5(t *testing.T) {
+	input := `0,9 -> 5,9
+8,0 -> 0,8
+9,4 -> 3,4
+2,2 -> 2,1
+7,0 -> 7,4
+6,4 -> 2,0
+0,9 -> 2,9
+3,4 -> 1,4
+0,0 -> 8,8
+5,5 -> 8,2`
+
+	assert.EqualValues(t, 5, D5(input))
+}

main.go

@@ -11,6 +11,7 @@ import (
 	"github.com/fotonmoton/aoc2021/d2"
 	"github.com/fotonmoton/aoc2021/d3"
 	"github.com/fotonmoton/aoc2021/d4"
+	"github.com/fotonmoton/aoc2021/d5"
 )
 
 func main() {
@@ -31,4 +32,5 @@ func main() {
 	fmt.Printf("day 3 part 2: %v\n", d3.D3P2(client.Day(3)))
 	fmt.Printf("day 4: %v\n", d4.D4(client.Day(4)))
 	fmt.Printf("day 4 part 2: %v\n", d4.D4P2(client.Day(4)))
+	fmt.Printf("day 5: %v\n", d5.D5(client.Day(5)))
 }