perf(2024): update day 4

believer · Dec 4, 2024 · 4bab4d6 · 4bab4d6
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diff --git a/go/2024/README.md b/go/2024/README.md
@@ -23,22 +23,23 @@ Collect stars by solving puzzles. Two puzzles will be made available on each day
 
 Using Go's built-in benchmarking with the [testing](https://pkg.go.dev/testing#hdr-Benchmarks) package. Computer is a 2021 MacBook Pro M1 Pro, 32 GB RAM.
 
-| Day |            #1 |           #2 | Improvement\*      |
-| --- | ------------: | -----------: | ------------------ |
-| 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   | 2864606 ns/op | 294413 ns/op |                    |
+| Day |           #1 |           #2 | Improvement\*      |
+| --- | -----------: | -----------: | ------------------ |
+| 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 | 294413 ns/op | `81.73%` / -       |
 
 \* compared to first solution
 
 ### Previous solutions
 
-| Day |           #1 |            #2 |  Improvement | Link                                                                                                                           |
-| --: | -----------: | ------------: | -----------: | ------------------------------------------------------------------------------------------------------------------------------ |
-|   1 | 120513 ns/op |  415683 ns/op |     Baseline | [Link](https://github.com/believer/advent-of-code/blob/47447cc17fffe6994d4b54c4cb815e698b3f5605/go/2024/puzzles/day01/main.go) |
-|   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) |
+| Day |            #1 |            #2 |  Improvement | Link                                                                                                                           |
+| --: | ------------: | ------------: | -----------: | ------------------------------------------------------------------------------------------------------------------------------ |
+|   1 |  120513 ns/op |  415683 ns/op |     Baseline | [Link](https://github.com/believer/advent-of-code/blob/47447cc17fffe6994d4b54c4cb815e698b3f5605/go/2024/puzzles/day01/main.go) |
+|   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) |
 
 ## Running
 

diff --git a/go/2024/puzzles/day04/main.go b/go/2024/puzzles/day04/main.go
@@ -2,13 +2,12 @@ package main
 
 import (
 	"fmt"
-	"regexp"
 	"strings"
 
 	"github.com/believer/aoc-2024/utils/files"
 )
 
-// Can be cleaned up a bunch, but it works!
+// Changed part 1 to take a similar approach to what I did in part 2
 func main() {
 	fmt.Println("Part 1: ", part1("input.txt"))
 	fmt.Println("Part 2: ", part2("input.txt"))
@@ -17,103 +16,45 @@ func main() {
 func part1(name string) int {
 	lines := files.ReadLines(name)
 	xmas := 0
-	forwards := regexp.MustCompile(`XMAS`)
-	backwards := regexp.MustCompile(`SAMX`)
-
-	// Check horizontal, forwards and backwards
-	for _, l := range lines {
-		t := len(forwards.FindAllString(l, -1))
-		t2 := len(backwards.FindAllString(l, -1))
-
-		xmas += t + t2
-	}
 
 	rows := len(lines)
 	cols := len(lines[0])
 
-	// Check vertical
-	for col := 0; col < cols; col++ {
-		vertical := ""
-
-		for row := 0; row < rows; row++ {
-			// Getting from line by row/col becomes an ASCII rune. Convert to string.
-			vertical += string(lines[row][col])
-		}
-
-		t := len(forwards.FindAllString(vertical, -1))
-		t2 := len(backwards.FindAllString(vertical, -1))
-
-		xmas += t + t2
-	}
-
-	// Diagonal, top-left to bottom-right
-	for start := 0; start < rows; start++ {
-		diagonal := ""
-
-		for i, j := start, 0; i < rows && j < cols; i, j = i+1, j+1 {
-			diagonal += string(lines[i][j])
-		}
-
-		if len(diagonal) < 4 {
-			break
-		}
-
-		t := len(forwards.FindAllString(diagonal, -1))
-		t2 := len(backwards.FindAllString(diagonal, -1))
-
-		xmas += t + t2
-	}
-
-	for start := 1; start < cols; start++ {
-		diagonal := ""
-
-		for i, j := 0, start; i < rows && j < cols; i, j = i+1, j+1 {
-			diagonal += string(lines[i][j])
-		}
-
-		if len(diagonal) < 4 {
-			break
-		}
-
-		t := len(forwards.FindAllString(diagonal, -1))
-		t2 := len(backwards.FindAllString(diagonal, -1))
-
-		xmas += t + t2
-	}
-
-	// Diagonal, top-right to bottom-left
-	for start := 0; start < rows; start++ {
-		diagonal := ""
-
-		for i, j := start, cols-1; i < rows && j >= 0; i, j = i+1, j-1 {
-			diagonal += string(lines[i][j])
-		}
+	for r := range rows {
+		for c := range cols {
+			// Skip if not an X
+			if string(lines[r][c]) != "X" {
+				continue
+			}
 
-		if len(diagonal) < 4 {
-			break
-		}
+			// Check all directions
+			for _, dr := range []int{-1, 0, 1} {
+				for _, dc := range []int{-1, 0, 1} {
+					if dr == 0 && dc == 0 {
+						continue
+					}
 
-		t := len(forwards.FindAllString(diagonal, -1))
-		t2 := len(backwards.FindAllString(diagonal, -1))
+					// Check bounds
+					threeDown := r + 3*dr
+					threeForwards := c + 3*dc
+					hasSpaceDown := threeDown >= 0 && threeDown < rows
+					hasSpaceForwards := threeForwards >= 0 && threeForwards < cols
 
-		xmas += t + t2
-	}
-
-	for start := cols - 2; start >= 0; start-- {
-		diagonal := ""
+					if !hasSpaceDown || !hasSpaceForwards {
+						continue
+					}
 
-		for i, j := 0, start; i < rows && j >= 0; i, j = i+1, j-1 {
-			diagonal += string(lines[i][j])
-		}
+					// 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 len(diagonal) < 4 {
-			break
+					if nextIsM && nextIsA && nextIsS {
+						xmas++
+					}
+				}
+			}
 		}
-
-		t := len(forwards.FindAllString(diagonal, -1))
-		t2 := len(backwards.FindAllString(diagonal, -1))
-
-		xmas += t + t2
 	}
 
 	return xmas
@@ -129,41 +70,43 @@ func part2(name string) int {
 	for i, r := range lines {
 		for j := range strings.Split(r, "") {
 			// A's are always in the middle
-			if string(r[j]) == "A" {
-				// Check line above and below
-				if i-1 >= 0 && j-1 >= 0 && i+1 < rows && j+1 < cols {
-					diagonalTopLeft := string(lines[i-1][j-1])
-					diagonalTopRight := string(lines[i-1][j+1])
-					diagonalBottomLeft := string(lines[i+1][j-1])
-					diagonalBottomRight := string(lines[i+1][j+1])
-
-					// M.M
-					// .A.
-					// S.S
-					if diagonalTopLeft == "M" && diagonalBottomRight == "S" && diagonalTopRight == "M" && diagonalBottomLeft == "S" {
-						xmas++
-					}
+			if string(r[j]) != "A" {
+				continue
+			}
 
-					// M.S
-					// .A.
-					// M.S
-					if diagonalTopLeft == "M" && diagonalBottomRight == "S" && diagonalTopRight == "S" && diagonalBottomLeft == "M" {
-						xmas++
-					}
+			// Check line above and below
+			if i-1 >= 0 && j-1 >= 0 && i+1 < rows && j+1 < cols {
+				diagonalTopLeft := string(lines[i-1][j-1])
+				diagonalTopRight := string(lines[i-1][j+1])
+				diagonalBottomLeft := string(lines[i+1][j-1])
+				diagonalBottomRight := string(lines[i+1][j+1])
+
+				// M.M
+				// .A.
+				// S.S
+				if diagonalTopLeft == "M" && diagonalBottomRight == "S" && diagonalTopRight == "M" && diagonalBottomLeft == "S" {
+					xmas++
+				}
 
-					// S.S
-					// .A.
-					// M.M
-					if diagonalTopLeft == "S" && diagonalBottomRight == "M" && diagonalTopRight == "S" && diagonalBottomLeft == "M" {
-						xmas++
-					}
+				// M.S
+				// .A.
+				// M.S
+				if diagonalTopLeft == "M" && diagonalBottomRight == "S" && diagonalTopRight == "S" && diagonalBottomLeft == "M" {
+					xmas++
+				}
 
-					// S.M
-					// .A.
-					// S.M
-					if diagonalTopLeft == "S" && diagonalBottomRight == "M" && diagonalTopRight == "M" && diagonalBottomLeft == "S" {
-						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++
 				}
 			}
 		}