perf(2024): improve day 4

Author: believer

go/2024/README.md

@@ -36,7 +36,7 @@ Using Go's built-in benchmarking with the [testing](https://pkg.go.dev/testing#h
 | 1   |    116264 ns/op |     131233 ns/op | `3.53%` / `68.43%`  |
 | 2   |    310935 ns/op |     723512 ns/op |                     |
 | 3   |    336448 ns/op |     785320 ns/op | - / `36.98%`        |
-| 4   |    523315 ns/op |     217584 ns/op | `81.73%` / `26.09%` |
+| 4   |    250981 ns/op |     110358 ns/op | `91.24%` / `62.52%` |
 | 5   |    778880 ns/op |    3129873 ns/op | `53.34%` / `81.91%` |
 | 6   |    312461 ns/op | 1153391125 ns/op |                     |
 | 7   |  16480300 ns/op |  842853000 ns/op | `87.01%` / `91.67%` |
@@ -56,6 +56,7 @@ Using Go's built-in benchmarking with the [testing](https://pkg.go.dev/testing#h
 |   1 |    120513 ns/op |      155479 ns/op |        - / `62,59%` | [Link](https://github.com/believer/advent-of-code/blob/ea42592462771b74de87eae6bea9c0ca892a4499/go/2024/puzzles/day01/main.go) |
 |   3 |    336448 ns/op |     1246155 ns/op |            Baseline | [Link](https://github.com/believer/advent-of-code/blob/461c2dd40039c27102aa1790c650decb79d4f549/go/2024/puzzles/day03/main.go) |
 |   4 |   2864606 ns/op |      294413 ns/op |            Baseline | [Link](https://github.com/believer/advent-of-code/blob/99909bb30f82cda079471134452d886a0eb6266f/go/2024/puzzles/day04/main.go) |
+|   4 |    523315 ns/op |      217584 ns/op | `81.73%` / `26.09%` | [Link](https://github.com/believer/advent-of-code/blob/431059e6b64faba3bc67c293b57ae299d3525bb9/go/2024/puzzles/day04/main.go) |
 |   5 |   1669175 ns/op |    17299190 ns/op |            Baseline | [Link](https://github.com/believer/advent-of-code/blob/1db858ae3d391319511787d8935c76eecdf6b22f/go/2024/puzzles/day05/main.go) |
 |   7 | 126892714 ns/op | 10124683583 ns/op |            Baseline | [Link](https://github.com/believer/advent-of-code/blob/dd735747021ce43ca3a7427c529813139737271e/go/2024/puzzles/day07/main.go) |
 |   7 | 110164692 ns/op |  7135839625 ns/op | `13.18%` / `29.52%` | [Link](https://github.com/believer/advent-of-code/blob/640d9604dfefa71f7bfef876750f378bd1a58a8b/go/2024/puzzles/day07/main.go) |

go/2024/puzzles/day04/main.go

@@ -4,6 +4,7 @@ import (
 	"fmt"
 
 	"github.com/believer/aoc-2024/utils/files"
+	"github.com/believer/aoc-2024/utils/grid"
 )
 
 // Changed part 1 to take a similar approach to what I did in part 2
@@ -14,43 +15,39 @@ func main() {
 
 func part1(name string) int {
 	lines := files.ReadLines(name)
+	xmasGrid := grid.New(lines)
 	xmas := 0
 
-	rows := len(lines)
-	cols := len(lines[0])
+	for y := range xmasGrid.Height {
+		for x := range xmasGrid.Width {
+			point := grid.Point{X: x, Y: y}
 
-	for r := range rows {
-		for c := range cols {
 			// Skip if not an X
-			if string(lines[r][c]) != "X" {
+			if xmasGrid.Get(point) != 'X' {
 				continue
 			}
 
 			// Check all directions
-			for _, dr := range []int{-1, 0, 1} {
-				for _, dc := range []int{-1, 0, 1} {
-					if dr == 0 && dc == 0 {
-						continue
-					}
-
-					// Check bounds
-					threeDown := r + 3*dr
-					threeForwards := c + 3*dc
-					hasSpaceDown := threeDown >= 0 && threeDown < rows
-					hasSpaceForwards := threeForwards >= 0 && threeForwards < cols
-
-					if !hasSpaceDown || !hasSpaceForwards {
-						continue
-					}
-
-					// Check that the next three letters are MAS
-					nextIsM := string(lines[r+dr][c+dc]) == "M"
-					nextIsA := string(lines[r+2*dr][c+2*dc]) == "A"
-					nextIsS := string(lines[r+3*dr][c+3*dc]) == "S"
-
-					if nextIsM && nextIsA && nextIsS {
-						xmas++
-					}
+			for _, d := range grid.ALL_DIRECTIONS {
+				dx, dy := d.X, d.Y
+
+				// Do we have enough items to check?
+				offByThree := grid.Point{X: x + 3*dx, Y: y + 3*dy}
+
+				if _, ok := xmasGrid.Contains(offByThree); !ok {
+					continue
+				}
+
+				offByOne := grid.Point{X: x + dx, Y: y + dy}
+				offByTwo := grid.Point{X: x + 2*dx, Y: y + 2*dy}
+
+				// Check that the next three letters are MAS
+				isM := xmasGrid.Get(offByOne) == 'M'
+				isA := xmasGrid.Get(offByTwo) == 'A'
+				isS := xmasGrid.Get(offByThree) == 'S'
+
+				if isM && isA && isS {
+					xmas++
 				}
 			}
 		}
@@ -61,53 +58,59 @@ func part1(name string) int {
 
 func part2(name string) int {
 	lines := files.ReadLines(name)
+	xmasGrid := grid.New(lines)
 	xmas := 0
 
-	rows := len(lines)
-	cols := len(lines[0])
-
 	// Skip checking edge characters since any A here can't result in a X-MAS
-	for r := range rows - 1 {
-		for c := range cols - 1 {
+	for y := range xmasGrid.Height - 1 {
+		for x := range xmasGrid.Width - 1 {
+			point := grid.Point{X: x, Y: y}
+
 			// A's are always in the middle
-			if string(lines[r][c]) != "A" {
+			if xmasGrid.Get(point) != 'A' {
+				continue
+			}
+
+			if _, ok := xmasGrid.Contains(point.Add(grid.TOPLEFT)); !ok {
+				continue
+			}
+
+			if _, ok := xmasGrid.Contains(point.Add(grid.BOTTOMRIGHT)); !ok {
 				continue
 			}
 
 			// Check line above and below
-			if r-1 >= 0 && c-1 >= 0 && r+1 < rows && c+1 < cols {
-				diagonalTopLeft := string(lines[r-1][c-1])
-				diagonalTopRight := string(lines[r-1][c+1])
-				diagonalBottomLeft := string(lines[r+1][c-1])
-				diagonalBottomRight := string(lines[r+1][c+1])
-
-				// M.M
-				// .A.
-				// S.S
-				if diagonalTopLeft == "M" && diagonalBottomRight == "S" && diagonalTopRight == "M" && diagonalBottomLeft == "S" {
-					xmas++
-				}
+			diagonalTopLeft := xmasGrid.Get(point.Add(grid.TOPLEFT))
+			diagonalTopRight := xmasGrid.Get(point.Add(grid.TOPRIGHT))
+			diagonalBottomLeft := xmasGrid.Get(point.Add(grid.BOTTOMLEFT))
+			diagonalBottomRight := xmasGrid.Get(point.Add(grid.BOTTOMRIGHT))
+
+			// M.M
+			// .A.
+			// S.S
+			if diagonalTopLeft == 'M' && diagonalBottomRight == 'S' && diagonalTopRight == 'M' && diagonalBottomLeft == 'S' {
+				xmas++
+			}
 
-				// M.S
-				// .A.
-				// M.S
-				if diagonalTopLeft == "M" && diagonalBottomRight == "S" && diagonalTopRight == "S" && diagonalBottomLeft == "M" {
-					xmas++
-				}
+			// M.S
+			// .A.
+			// M.S
+			if diagonalTopLeft == 'M' && diagonalBottomRight == 'S' && diagonalTopRight == 'S' && diagonalBottomLeft == 'M' {
+				xmas++
+			}
 
-				// S.S
-				// .A.
-				// M.M
-				if diagonalTopLeft == "S" && diagonalBottomRight == "M" && diagonalTopRight == "S" && diagonalBottomLeft == "M" {
-					xmas++
-				}
+			// S.S
+			// .A.
+			// M.M
+			if diagonalTopLeft == 'S' && diagonalBottomRight == 'M' && diagonalTopRight == 'S' && diagonalBottomLeft == 'M' {
+				xmas++
+			}
 
-				// S.M
-				// .A.
-				// S.M
-				if diagonalTopLeft == "S" && diagonalBottomRight == "M" && diagonalTopRight == "M" && diagonalBottomLeft == "S" {
-					xmas++
-				}
+			// S.M
+			// .A.
+			// S.M
+			if diagonalTopLeft == 'S' && diagonalBottomRight == 'M' && diagonalTopRight == 'M' && diagonalBottomLeft == 'S' {
+				xmas++
 			}
 		}
 	}

go/2024/utils/grid/grid.go

@@ -13,7 +13,22 @@ var UP = Point{0, -1}
 var DOWN = Point{0, 1}
 var RIGHT = Point{1, 0}
 var LEFT = Point{-1, 0}
+var TOPLEFT = Point{-1, -1}
+var TOPRIGHT = Point{1, -1}
+var BOTTOMLEFT = Point{-1, 1}
+var BOTTOMRIGHT = Point{1, 1}
+
 var CARDINALS = []Point{UP, DOWN, LEFT, RIGHT}
+var ALL_DIRECTIONS = []Point{
+	TOPLEFT,
+	UP,
+	TOPRIGHT,
+	RIGHT,
+	BOTTOMRIGHT,
+	DOWN,
+	BOTTOMLEFT,
+	LEFT,
+}
 
 func (p *Point) Add(p2 Point) Point {
 	return Point{p.X + p2.X, p.Y + p2.Y}