Completed part 2 of Day 22 puzzle (with a lot of help from Go code of rumkugel13 to correct my 2 bugs)

day22/day22.go

@@ -105,6 +105,13 @@ func (tower *Tower) layout(brick *Brick, currZ int) {
 			}
 		}
 	}
+
+	brick.start.z = currZ
+	if brickHeight > 1 {
+		brick.end.z = currZ + brickHeight - 1
+	} else {
+		brick.end.z = currZ
+	}
 }
 
 func (tower *Tower) addBrick(brick *Brick) {
@@ -137,11 +144,11 @@ func (tower *Tower) addBrick(brick *Brick) {
 
 func (tower *Tower) Print() {
 	//for z := tower.maxHeight(); z >= 0; z-- {
-	for z := 8; z > 0; z-- {
+	for z := 20; z > 0; z-- {
 		for x := 0; x < tower.floorWidth; x++ {
 			for y := 0; y < tower.floorWidth; y++ {
 				if tower.floors[z][x][y] != nil {
-					fmt.Print(tower.floors[z][x][y].ID)
+					fmt.Print(string(byte('A') - 1 + byte(tower.floors[z][x][y].ID)%26))
 				} else {
 					fmt.Print(".")
 				}
@@ -184,3 +191,141 @@ func Part1(lines []string) (int, []*Brick) {
 	tower.Print()
 	return count, bricks
 }
+
+/*
+func Part2(lines []string) {
+	// place bricks like Part1
+	// and change z coord of each brick once it is layed out
+	bricks := parseBricks(lines)
+	tower := NewTower(500, 10)
+
+	for _, brick := range bricks {
+		fmt.Printf("Placing brick %d (%v)~(%v)\n", brick.ID, brick.start, brick.end)
+		tower.addBrick(brick)
+	}
+
+	// sort brick by z coord desc (highest first)
+	slices.SortFunc(bricks, func(a, b *Brick) int {
+		return b.start.z - a.start.z
+	})
+
+	// for each brick
+	//    if the brick above the current brick has just the current brick as support
+	//    then add 1 + the total fall of the brick above (coming from the map "total fallen")
+	//    Store the value in the map "total fallen" using the ID of the current brick
+	// end for
+	count := 0
+	for _, brick := range bricks {
+		for _, aboveBrick := range brick.supports {
+			if len(aboveBrick.supportedBy) == 0 {
+				log.Fatalln("Bug ", brick)
+			}
+			if len(aboveBrick.supportedBy) == 1 {
+				// will fall
+
+			}
+		}
+	}
+
+}
+*/
+
+func buildDropList(brick *Brick, droppedList *map[int]bool) {
+	// Do not drop if the bricks below have not all been removed
+	for _, supportedBy := range brick.supportedBy {
+		if !(*droppedList)[supportedBy.ID] {
+			return
+		}
+	}
+
+	(*droppedList)[brick.ID] = true // the supported brick
+
+	for _, supportedBrick := range brick.supports {
+		dropAbove := true
+		for _, supportedBy := range supportedBrick.supportedBy {
+			if !(*droppedList)[supportedBy.ID] {
+				dropAbove = false
+			}
+		}
+		if dropAbove {
+			buildDropList(supportedBrick, droppedList) // the drops from the supported brick
+		}
+	}
+}
+
+func Part2(lines []string) int {
+	bricks := parseBricks(lines)
+	tower := NewTower(500, 10)
+
+	for _, brick := range bricks {
+		//fmt.Printf("Placing brick %d (%v)~(%v)\n", brick.ID, brick.start, brick.end)
+		tower.addBrick(brick)
+	}
+
+	// for debugging
+	slices.SortFunc(bricks, func(a, b *Brick) int {
+		return a.ID - b.ID
+	})
+
+	sum := 0
+	for _, brick := range bricks {
+		singleSupport := false
+
+		for _, supportedBrick := range brick.supports {
+			if len(supportedBrick.supportedBy) == 0 {
+				log.Fatalln("Bug ", brick)
+			}
+			if len(supportedBrick.supportedBy) == 1 {
+				singleSupport = true
+			}
+		}
+		/*
+				if singleSupport {
+
+					disintegrated := map[int]bool{brick.ID: true}
+					checkList := []*Brick{brick}
+					for len(checkList) > 0 {
+						// take first from checklist
+						check := checkList[0]
+						checkList = checkList[1:]
+						// for all bricks above, check ...
+						for _, above := range check.supports {
+							bricksRemoved := 0
+							// whether all bricks below it are disintegrated ...
+							for _, below := range above.supportedBy {
+								if disintegrated[below.ID] {
+									bricksRemoved++
+								}
+							}
+							if len(above.supportedBy) == bricksRemoved {
+								// then it would fall
+								checkList = append(checkList, above)
+								disintegrated[above.ID] = true
+							}
+						}
+					}
+					// do not include the brick we are currently checking
+					fmt.Printf("Brick %d would drop %d other bricks\n", brick.ID, len(disintegrated)-1)
+					sum += len(disintegrated) - 1
+				}
+			}
+		*/
+
+		if singleSupport {
+			dropList := map[int]bool{}
+			dropList[brick.ID] = true
+			if brick.ID == 14 {
+				fmt.Println("debug")
+			}
+			for _, supportedBrick := range brick.supports {
+				buildDropList(supportedBrick, &dropList)
+			}
+			fmt.Printf("Brick %d would drop %d other bricks\n", brick.ID, len(dropList)-1)
+			sum += len(dropList) - 1
+		}
+	}
+
+	tower.Print()
+
+	return sum
+}

day22/day22_test.go

@@ -35,3 +35,31 @@ func TestPart1WithInput(t *testing.T) {
 		t.Fatalf("expected 428, got %d", result)
 	}
 }
+
+func TestPart2(t *testing.T) {
+	lines := []string{
+		"1,0,1~1,2,1", // 1
+		"0,0,2~2,0,2", // 2
+		"0,2,3~2,2,3", // 3
+		"0,0,4~0,2,4", // 4
+		"2,0,5~2,2,5", // 5
+		"0,1,6~2,1,6", // 6
+		"1,1,8~1,1,9", // 7
+	}
+
+	result := Part2(lines)
+
+	if result != 7 {
+		t.Fatalf("expected 7, got %d", result)
+	}
+}
+
+func TestPart2WithInput(t *testing.T) {
+	lines := utils.ReadLines("input.txt")
+
+	result := Part2(lines)
+
+	if result != 35654 {
+		t.Fatalf("expected 35654, got %d", result)
+	}
+}