Day 24: Part 2

The search is _not_ fast since it scales as the tiles move away from each other. Should been more clever about the search space ¯\_(ツ)_/¯

Signed-off-by: James Griffin <james@unsupervised.ca>

main.go

@@ -101,4 +101,5 @@ func main() {
 
 	// Day 24
 	fmt.Println(twentyfour.PartOne())
+	fmt.Println(twentyfour.PartTwo())
 }

twentyfour/day_twentyfour.go

@@ -83,6 +83,79 @@ func (l *lobby) countTiles() (black, white int) {
 	return black, white
 }
 
+func (l *lobby) dailyFlip(days int) {
+	for i := 0; i < days; i++ {
+		fmt.Println("Day", i+1)
+		newGrid := map[string]bool{}
+
+		xMin, yMin, zMin, xMax, yMax, zMax := 0, 0, 0, 0, 0, 0
+		for index := range l.tiles {
+			var x, y, z int
+			fmt.Sscanf(index, "%d,%d,%d", &x, &y, &z)
+			if x < xMin {
+				xMin = x
+			}
+			if x > xMax {
+				xMax = x
+			}
+
+			if y < yMin {
+				yMin = y
+			}
+
+			if y > yMax {
+				yMax = y
+			}
+
+			if z < zMin {
+				zMin = z
+			}
+
+			if z > zMax {
+				zMax = z
+			}
+		}
+
+		for x := xMin - 1; x <= xMax+1; x++ {
+			for y := yMin - 1; y <= yMax+1; y++ {
+				for z := zMin - 1; z <= zMax+1; z++ {
+					blackNeighbours := 0
+					if l.tiles[fmt.Sprintf("%d,%d,%d", x+1, y, z-1)] {
+						blackNeighbours++
+					}
+					if l.tiles[fmt.Sprintf("%d,%d,%d", x+1, y-1, z)] {
+						blackNeighbours++
+					}
+					if l.tiles[fmt.Sprintf("%d,%d,%d", x, y-1, z+1)] {
+						blackNeighbours++
+					}
+					if l.tiles[fmt.Sprintf("%d,%d,%d", x-1, y, z+1)] {
+						blackNeighbours++
+					}
+					if l.tiles[fmt.Sprintf("%d,%d,%d", x-1, y+1, z)] {
+						blackNeighbours++
+					}
+					if l.tiles[fmt.Sprintf("%d,%d,%d", x, y+1, z-1)] {
+						blackNeighbours++
+					}
+
+					index := fmt.Sprintf("%d,%d,%d", x, y, z)
+					if l.tiles[index] {
+						if blackNeighbours > 0 && blackNeighbours < 3 {
+							newGrid[index] = true
+						}
+					} else {
+						if blackNeighbours == 2 {
+							newGrid[index] = true
+						}
+					}
+				}
+			}
+		}
+		l.tiles = newGrid
+	}
+}
+
 // PartOne How many tiles are left black
 func PartOne() string {
 	l := lobby{}
@@ -93,3 +166,15 @@ func PartOne() string {
 
 	return fmt.Sprintf("There are %d black tiles", black)
 }
+
+// PartTwo How many tiles are black after 100 days
+func PartTwo() string {
+	l := lobby{}
+	l.load("twentyfour/input.txt")
+
+	l.layout()
+	l.dailyFlip(100)
+	black, _ := l.countTiles()
+
+	return fmt.Sprintf("There are %d black tiles", black)
+}

twentyfour/day_twentyfour_test.go

@@ -38,3 +38,72 @@ func Test_layout_tiles(t *testing.T) {
 		t.Fail()
 	}
 }
+
+func Test_daily_flip(t *testing.T) {
+	l := lobby{}
+	l.load("sample.txt")
+
+	l.layout()
+	black, white := l.countTiles()
+	if black+white != 15 {
+		t.Logf("Expected 15 tiles, got %d", black+white)
+		t.Fail()
+	}
+
+	if black != 10 {
+		t.Logf("Expected 10 black tiles, got %d", black)
+		t.Fail()
+	}
+
+	l.dailyFlip(1)
+	black, _ = l.countTiles()
+	if black != 15 {
+		t.Logf("Expected 15 black tiles, got %d", black)
+		t.FailNow()
+	}
+
+	l.dailyFlip(1)
+	black, _ = l.countTiles()
+	if black != 12 {
+		t.Logf("Expected 12 black tiles, got %d", black)
+		t.FailNow()
+	}
+
+	l.dailyFlip(1)
+	black, _ = l.countTiles()
+	if black != 25 {
+		t.Logf("Expected 25 black tiles, got %d", black)
+		t.FailNow()
+	}
+
+	l.dailyFlip(1)
+	black, _ = l.countTiles()
+	if black != 14 {
+		t.Logf("Expected 14 black tiles, got %d", black)
+		t.FailNow()
+	}
+}
+
+func Test_flip(t *testing.T) {
+	l := lobby{}
+	l.load("sample.txt")
+
+	l.layout()
+	black, white := l.countTiles()
+	if black+white != 15 {
+		t.Logf("Expected 15 tiles, got %d", black+white)
+		t.Fail()
+	}
+
+	if black != 10 {
+		t.Logf("Expected 10 black tiles, got %d", black)
+		t.Fail()
+	}
+
+	l.dailyFlip(100)
+	black, _ = l.countTiles()
+	if black != 2208 {
+		t.Logf("Expected 2208 black tiles, got %d", black)
+		t.FailNow()
+	}
+}