Added 12. part 2. fast (10x) solution

day_12/solution.go

@@ -47,16 +47,16 @@ func SolveBasic(input string) int {
 					// mark as visited to not visit it more than once
 					visited[point] = true
 
-					if _, present := field[Point{point.x - 1, point.y}]; !present {
+					if farmMap.At(point.x-1, point.y) != value {
 						parameter++
 					}
-					if _, present := field[Point{point.x + 1, point.y}]; !present {
+					if farmMap.At(point.x+1, point.y) != value {
 						parameter++
 					}
-					if _, present := field[Point{point.x, point.y - 1}]; !present {
+					if farmMap.At(point.x, point.y-1) != value {
 						parameter++
 					}
-					if _, present := field[Point{point.x, point.y + 1}]; !present {
+					if farmMap.At(point.x, point.y+1) != value {
 						parameter++
 					}
 				}
@@ -96,6 +96,35 @@ func SolveComplex(input string) int {
 	return sum
 }
 
+// task:https://adventofcode.com/2024/day/12#part2
+// there is no need to iterate over the whole table,
+// more importantly there is no need to look at the set as we at the Map
+func SolveComplexFast(input string) int {
+	farmMap := loadMap(input)
+	visited := Visited{}
+
+	sum := 0
+
+	for y, row := range farmMap {
+		for x, value := range row {
+			p := Point{x, y}
+			field := Visited{}
+			if _, present := visited[p]; !present {
+				visit(farmMap, field, x, y, value)
+				area := len(field)
+				parameter := countEdgesFast(farmMap, field, value)
+
+				for point := range field {
+					// mark as visited to not visit it more than once
+					visited[point] = true
+				}
+				sum += area * parameter
+			}
+		}
+	}
+	return sum
+}
+
 func countEdges(farmMap Map, field Visited) int {
 	borders := map[BorderPoint]bool{}
 	edges := 0
@@ -133,6 +162,49 @@ func countEdges(farmMap Map, field Visited) int {
 	return edges
 }
 
+func countEdgesFast(farmMap Map, field Visited, value rune) int {
+	edges := 0
+
+	for p := range field {
+		hasN := farmMap.At(p.x, p.y-1) == value
+		hasW := farmMap.At(p.x-1, p.y) == value
+		hasS := farmMap.At(p.x, p.y+1) == value
+		hasE := farmMap.At(p.x+1, p.y) == value
+		hasNW := farmMap.At(p.x-1, p.y-1) == value
+		hasNE := farmMap.At(p.x+1, p.y-1) == value
+		hasSW := farmMap.At(p.x-1, p.y+1) == value
+		hasSE := farmMap.At(p.x+1, p.y+1) == value
+
+		// inner corner
+		if hasN && hasW && !hasNW {
+			edges++
+		}
+		if hasN && hasE && !hasNE {
+			edges++
+		}
+		if hasS && hasW && !hasSW {
+			edges++
+		}
+		if hasS && hasE && !hasSE {
+			edges++
+		}
+		// outer corner
+		if !hasN && !hasW {
+			edges++
+		}
+		if !hasN && !hasE {
+			edges++
+		}
+		if !hasS && !hasW {
+			edges++
+		}
+		if !hasS && !hasE {
+			edges++
+		}
+	}
+	return edges
+}
+
 type Direction int
 
 const (