speed up day 5 with preallocated slices, not a map

05/main.go

@@ -42,12 +42,15 @@ type point struct {
 }
 
 type grid struct {
-	m map[point]int
+	m [][]int
 }
 
 func (g *grid) AddLine(start, end point, includeHorizontal bool) {
 	for _, p := range LineFromPoints(start, end, includeHorizontal) {
-		g.m[p]++
+		if g.m[p.x] == nil {
+			g.m[p.x] = make([]int, 1000)
+		}
+		g.m[p.x][p.y]++
 	}
 }
 
@@ -109,7 +112,7 @@ func partOne() {
 	scanner := makeScanner(false)
 
 	grid := &grid{
-		m: map[point]int{},
+		m: make([][]int, 1000),
 	}
 	for scanner.Scan() {
 		line := scanner.Text()
@@ -118,8 +121,10 @@ func partOne() {
 	}
 	var danger int
 	for i := range grid.m {
-		if grid.m[i] > 1 {
-			danger++
+		for j := range grid.m[i] {
+			if grid.m[i][j] > 1 {
+				danger++
+			}
 		}
 	}
 	fmt.Println(danger)
@@ -129,7 +134,7 @@ func partTwo() {
 	scanner := makeScanner(false)
 
 	grid := &grid{
-		m: map[point]int{},
+		m: make([][]int, 1000),
 	}
 	for scanner.Scan() {
 		line := scanner.Text()
@@ -138,8 +143,10 @@ func partTwo() {
 	}
 	var danger int
 	for i := range grid.m {
-		if grid.m[i] > 1 {
-			danger++
+		for j := range grid.m[i] {
+			if grid.m[i][j] > 1 {
+				danger++
+			}
 		}
 	}
 	fmt.Println(danger)