Add solution for day 8 part 2

Author: terminalnode

solutions/day08/main.go

@@ -7,7 +7,7 @@ import (
 )
 
 func main() {
-	common.Setup(8, part1, nil)
+	common.Setup(8, part1, part2)
 }
 
 func part1(
@@ -51,3 +51,69 @@ func part1(
 
 	return fmt.Sprintf("Unique anti nodes: %d", len(antiNodeSet))
 }
+
+func part2(
+	input string,
+) string {
+	m, err := util.NewCharMatrix(input)
+	if err != nil {
+		return fmt.Sprintf("Failed to parse input: %v", err)
+	}
+
+	coords := make(map[uint8][]util.Coordinate)
+	for x := 0; x <= m.MaxX; x++ {
+		for y := 0; y <= m.MaxY; y++ {
+			char, _ := m.Get(x, y)
+			if char == '.' {
+				continue
+			}
+			coords[char] = append(coords[char], util.Coordinate{X: x, Y: y})
+		}
+	}
+
+	antiNodeSet := make(map[string]bool)
+	for _, charCoords := range coords {
+		for i, thisCoord := range charCoords {
+			if len(charCoords) > 1 {
+				addCoordinateToSet(antiNodeSet, thisCoord.X, thisCoord.Y)
+			}
+
+			for _, otherCoord := range charCoords[i+1:] {
+				xDiff := thisCoord.X - otherCoord.X
+				yDiff := thisCoord.Y - otherCoord.Y
+
+				for n := 1; true; n++ {
+					newX := thisCoord.X + (xDiff * n)
+					newY := thisCoord.Y + (yDiff * n)
+					if !m.IsInMatrix(newX, newY) {
+						break
+					}
+
+					addCoordinateToSet(antiNodeSet, newX, newY)
+				}
+
+				for n := 1; true; n++ {
+					newX := otherCoord.X - (xDiff * n)
+					newY := otherCoord.Y - (yDiff * n)
+					if !m.IsInMatrix(newX, newY) {
+						break
+					}
+
+					addCoordinateToSet(antiNodeSet, newX, newY)
+				}
+
+			}
+		}
+	}
+
+	return fmt.Sprintf("Unique anti nodes (with resonance): %d", len(antiNodeSet))
+}
+
+func addCoordinateToSet(
+	set map[string]bool,
+	x int,
+	y int,
+) {
+	key := fmt.Sprintf("%02d,%02d", x, y)
+	set[key] = true
+}