From 9b3cd9200ebeba744e532c43cd7dcbba2c0f400a Mon Sep 17 00:00:00 2001
From: Thomas Voss <mail@thomasvoss.com>
Date: Wed, 4 Dec 2024 06:57:27 +0100
Subject: Add solutions for 2024 day 4

---
 2024/04/puzzles.go | 88 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 88 insertions(+)
 create mode 100644 2024/04/puzzles.go

(limited to '2024/04/puzzles.go')

diff --git a/2024/04/puzzles.go b/2024/04/puzzles.go
new file mode 100644
index 0000000..eca88a2
--- /dev/null
+++ b/2024/04/puzzles.go
@@ -0,0 +1,88 @@
+package main
+
+import (
+	"bufio"
+	"fmt"
+	"log"
+	"os"
+)
+
+func main() {
+	f, err := os.Open("input")
+	if err != nil {
+		log.Fatal(err)
+	}
+	defer f.Close()
+
+	sc := bufio.NewScanner(f)
+	fmt.Println(xmasCnt(parseInput(sc)))
+}
+
+func parseInput(sc *bufio.Scanner) [][]rune {
+	var data [][]rune
+	for sc.Scan() {
+		row := make([]rune, 0, 140)
+		for _, ch := range sc.Text() {
+			row = append(row, ch)
+		}
+		data = append(data, row)
+	}
+	return data
+}
+
+// START PART 1
+func xmasCnt(data [][]rune) int {
+	cnt := 0
+	for i := range data {
+		for j := range data[i] {
+			coords := [...][8]int{
+				{i, j, i+1, j, i+2, j, i+3, j},       // Vertical;   top-down
+				{i, j, i-1, j, i-2, j, i-3, j},       // Vertical;   down-top
+				{i, j, i, j+1, i, j+2, i, j+3},       // Horizontal; left-right
+				{i, j, i, j-1, i, j-2, i, j-3},       // Horizontal; left-right
+				{i, j, i-1, j+1, i-2, j+2, i-3, j+3}, // Diagonal; bl-tr
+				{i, j, i+1, j+1, i+2, j+2, i+3, j+3}, // Diagonal; tl-br
+				{i, j, i+1, j-1, i+2, j-2, i+3, j-3}, // Diagonal; tr-bl
+				{i, j, i-1, j-1, i-2, j-2, i-3, j-3}, // Diagonal; br-tl
+			}
+			for _, x := range coords {
+				if x[0] >= 0 && x[0] < len(data) &&
+				x[2] >= 0 && x[2] < len(data) &&
+				x[4] >= 0 && x[4] < len(data) &&
+				x[6] >= 0 && x[6] < len(data) &&
+				x[1] >= 0 && x[1] < len(data[0]) &&
+				x[3] >= 0 && x[3] < len(data[0]) &&
+				x[5] >= 0 && x[5] < len(data[0]) &&
+				x[7] >= 0 && x[7] < len(data[0]) &&
+				data[x[0]][x[1]] == 'X' &&
+				data[x[2]][x[3]] == 'M' &&
+				data[x[4]][x[5]] == 'A' &&
+				data[x[6]][x[7]] == 'S' {
+					cnt++
+				}
+			}
+		}
+	}
+	return cnt
+}
+// END PART 1 START PART 2
+func xmasCnt(data [][]rune) int {
+	cnt := 0
+	for i := range data {
+		for j := range data[i] {
+			if data[i][j] != 'A' ||
+			i == 0 || i == len(data) - 1 ||
+			j == 0 || j == len(data[0]) - 1 {
+				continue
+			}
+			x1 := []rune{data[i-1][j-1], data[i+1][j+1]}
+			x2 := []rune{data[i+1][j-1], data[i-1][j+1]}
+			if (((x1[0] == 'S' && x1[1] == 'M') || (x1[0] == 'M' && x1[1] == 'S')) &&
+			    ((x2[0] == 'S' && x2[1] == 'M') || (x2[0] == 'M' && x2[1] == 'S'))) {
+				cnt++
+			}
+		}
+	}
+	return cnt
+}
+// END PART 2
\ No newline at end of file
-- 
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