Yes

Author: DWethmar

day09/main.go

@@ -4,6 +4,7 @@ import (
 	"fmt"
 	"io"
 	"log"
+	"math"
 	"os"
 	"strconv"
 	"strings"
@@ -13,6 +14,10 @@ type Point struct {
 	X, Y int
 }
 
+func (c *Point) String() string {
+	return fmt.Sprintf("%d,%d", c.X, c.Y)
+}
+
 func main() {
 	positionVisitedByTail, err := MoveRope(os.Stdin, (len(os.Args) >= 2 && os.Args[1] == "debug"))
 	if err != nil {
@@ -28,6 +33,8 @@ func MoveRope(input io.Reader, debug bool) (positionVisitedByTail int, err error
 
 	positionsVisited := []*Point{}
 
+	pointsVisited := map[string]struct{}{}
+
 	err = IterateLines(input, func(s string) Step {
 		direction := ""
 		distance := 0
@@ -52,13 +59,20 @@ func MoveRope(input io.Reader, debug bool) (positionVisitedByTail int, err error
 
 			move := DrawGrid(head, tail, []*Point{})
 
-			x, y := Follow(tail, head)
-			tail.X += x
-			tail.Y += y
+			// x := tail.X
+			// y := tail.Y
+
+			Follow(head, tail)
 
-			if x != 0 || y != 0 { // tail moved
+			// if x != tail.X || y != tail.Y { // tail moved
+			// 	positionsVisited = append(positionsVisited, &Point{X: tail.X, Y: tail.Y})
+			// 	positionVisitedByTail++
+			// }
+
+			if _, ok := pointsVisited[tail.String()]; !ok {
+				pointsVisited[tail.String()] = struct{}{}
 				positionsVisited = append(positionsVisited, &Point{X: tail.X, Y: tail.Y})
-				positionVisitedByTail++
+				positionVisitedByTail = len(positionsVisited)
 			}
 
 			if debug {
@@ -78,6 +92,42 @@ func MoveRope(input io.Reader, debug bool) (positionVisitedByTail int, err error
 	return
 }
 
+func Follow(head *Point, tail *Point) {
+	// If the head is right next to or directly on top of the tail then we do nothing
+	diffInX := math.Abs(float64(tail.X - head.X))
+	diffInY := math.Abs(float64(tail.Y - head.Y))
+
+	if diffInY <= 1 && diffInX <= 1 {
+		return
+	}
+
+	//fmt.Println(fmt.Sprintf("Tail moving (%s) to meet head (%s)", tail.String(), head.String()))
+	xDirection := 1
+	yDirection := 1
+
+	if head.Y < tail.Y {
+		yDirection = -1
+	}
+
+	if head.X < tail.X {
+		xDirection = -1
+	}
+
+	if head.X == tail.X {
+		tail.Y += 1 * yDirection
+		return
+	}
+
+	if head.Y == tail.Y {
+		tail.X += 1 * xDirection
+		return
+	}
+
+	// Diagonal
+	tail.X += 1 * xDirection
+	tail.Y += 1 * yDirection
+}
+
 func DrawGrid(head *Point, tail *Point, otherPoints []*Point) *strings.Builder {
 	var strBuilder = &strings.Builder{}
 
@@ -114,33 +164,3 @@ func DrawGrid(head *Point, tail *Point, otherPoints []*Point) *strings.Builder {
 
 	return strBuilder
 }
-
-func Follow(point *Point, target *Point) (x, y int) {
-	// only follow if distance between two point is greater then 1
-	if point.X == target.X && point.Y == target.Y {
-		return 0, 0
-	}
-
-	// check if adjacent
-	for tx := -1; tx <= 1; tx++ {
-		for ty := -1; ty <= 1; ty++ {
-			if point.X+tx == target.X && point.Y+ty == target.Y {
-				return 0, 0
-			}
-		}
-	}
-
-	if point.X < target.X {
-		x = 1
-	} else if point.X > target.X {
-		x = -1
-	}
-
-	if point.Y < target.Y {
-		y = 1
-	} else if point.Y > target.Y {
-		y = -1
-	}
-
-	return
-}

day09/main_test.go

@@ -64,6 +64,34 @@ func TestMoveRope(t *testing.T) {
 			wantErr:                          false,
 		},
 		// {
+		// 	name: "example",
+		// 	args: args{
+		// 		input: strings.NewReader(strings.Join([]string{
+		// 			"U 1",
+		// 			"R 1",
+		// 			"U 1",
+		// 			"R 1",
+		// 			"U 1",
+		// 			"R 3",
+		// 		}, "\n")),
+		// 		debug: true,
+		// 	},
+		// 	wantUniquePositionsVisitedByTail: 13,
+		// 	wantErr:                          false,
+		// },
+		// {
+		// 	name: "example",
+		// 	args: args{
+		// 		input: strings.NewReader(strings.Join([]string{
+		// 			"U 3",
+		// 			"R 2",
+		// 		}, "\n")),
+		// 		debug: true,
+		// 	},
+		// 	wantUniquePositionsVisitedByTail: 13,
+		// 	wantErr:                          false,
+		// },
+		// {
 		// 	name: "example2",
 		// 	args: args{
 		// 		input: strings.NewReader(testInput2),
@@ -120,7 +148,10 @@ func TestFollow(t *testing.T) {
 	}
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
-			gotX, gotY := Follow(tt.args.point, tt.args.target)
+			Follow(tt.args.point, tt.args.target)
+			gotX := tt.args.point.X
+			gotY := tt.args.point.Y
+
 			if gotX != tt.wantX {
 				t.Errorf("Follow() gotX = %v, want %v", gotX, tt.wantX)
 			}