feat: solve part seven day two

cmd/07/main.go

@@ -6,6 +6,7 @@ import (
 	"github.com/StevanFreeborn/advent-of-code-2025/internal/move"
 	"github.com/StevanFreeborn/advent-of-code-2025/internal/position"
 	"github.com/StevanFreeborn/advent-of-code-2025/internal/queue"
+	"github.com/StevanFreeborn/advent-of-code-2025/internal/stack"
 )
 
 const StartCharacter = "S"
@@ -68,3 +69,79 @@ func SolvePartOne(filePath string) int {
 
 	return total
 }
+
+func SolvePartTwo(filePath string) int {
+	input := file.ReadAllLines(filePath)
+	grid := grid.From(input)
+
+	var startPosition position.Position
+
+	for p, v := range grid.Positions() {
+		if v == StartCharacter {
+			startPosition = p
+			break
+		}
+	}
+
+	if startPosition == nil {
+		panic("unable to find start location")
+	}
+
+	beamStartPosition := startPosition.Move(move.Down)
+	beamsStack := stack.New[position.Position]()
+	beamsStack.Push(beamStartPosition)
+
+	positionsToTimelinesMap := map[position.Position]int{}
+
+	for beamsStack.IsEmpty() == false {
+		currentBeam, _ := beamsStack.Peek()
+
+		_, hasBeenProcessed := positionsToTimelinesMap[currentBeam]
+
+		if hasBeenProcessed {
+			beamsStack.Pop()
+			continue
+		}
+
+		value := grid.GetValueAt(currentBeam)
+		nextTimelinePositions := []position.Position{}
+
+		if value == SplitterCharacter {
+			rightBeam := currentBeam.Move(move.Right)
+			leftBeam := currentBeam.Move(move.Left)
+			nextTimelinePositions = append(nextTimelinePositions, rightBeam, leftBeam)
+		} else {
+			nextBeam := currentBeam.Move(move.Down)
+			nextTimelinePositions = append(nextTimelinePositions, nextBeam)
+		}
+
+		numberOfTimelinesForPosition := 0
+		finalizePosition := true
+
+		for _, newTimelinePosition := range nextTimelinePositions {
+			if grid.InBounds(newTimelinePosition) == false {
+				numberOfTimelinesForPosition++
+				continue
+			}
+
+			v, existing := positionsToTimelinesMap[newTimelinePosition]
+
+			if existing {
+				numberOfTimelinesForPosition += v
+				continue
+			}
+
+			beamsStack.Push(newTimelinePosition)
+			finalizePosition = false
+		}
+
+		if finalizePosition == false {
+			continue
+		}
+
+		beamsStack.Pop()
+		positionsToTimelinesMap[currentBeam] = numberOfTimelinesForPosition
+	}
+
+	return positionsToTimelinesMap[beamStartPosition]
+}

cmd/07/main_test.go

@@ -25,3 +25,23 @@ func TestSolvePartOneWithInput(t *testing.T) {
 		t.Errorf("SolvePartOne() = %d; want %d", result, expected)
 	}
 }
+
+func TestSolvePartTwoWithExampleInput(t *testing.T) {
+	expected := 40
+
+	result := solution.SolvePartTwo("EXAMPLE.txt")
+
+	if result != expected {
+		t.Errorf("SolveTwoOne() = %d; want %d", result, expected)
+	}
+}
+
+func TestSolvePartTwoWithInput(t *testing.T) {
+	expected := 73_007_003_089_792
+
+	result := solution.SolvePartTwo("INPUT.txt")
+
+	if result != expected {
+		t.Errorf("SolveTwoOne() = %d; want %d", result, expected)
+	}
+}