2024 day 4

Author: lucianoq

2024/4/Makefile

@@ -0,0 +1,17 @@
+main1:
+	go build -o main1 main1.go common.go
+
+main2:
+	go build -o main2 main2.go common.go
+
+.PHONY: run1 run2 clean
+
+run1: main1
+	./main1 <input
+
+run2: main2
+	./main2 <input
+
+clean:
+	rm -f main1 main2
+

2024/4/common.go

@@ -0,0 +1,25 @@
+package main
+
+import (
+	"bufio"
+	"os"
+)
+
+const Size = 140
+
+type P struct{ x, y int }
+
+func (p P) Add(d P, times int) P { return P{p.x + times*d.x, p.y + times*d.y} }
+
+func input() map[P]byte {
+	scanner := bufio.NewScanner(os.Stdin)
+
+	out := map[P]byte{}
+	for i := 0; scanner.Scan(); i++ {
+		line := scanner.Text()
+		for j := 0; j < len(line); j++ {
+			out[P{i, j}] = line[j]
+		}
+	}
+	return out
+}

2024/4/main1.go

@@ -0,0 +1,29 @@
+package main
+
+import "fmt"
+
+func main() {
+	m := input()
+	count := 0
+	for x := 0; x < Size; x++ {
+		for y := 0; y < Size; y++ {
+			for dx := -1; dx <= 1; dx++ {
+				for dy := -1; dy <= 1; dy++ {
+					if dx != 0 || dy != 0 {
+						if findXMas(m, P{x, y}, P{dx, dy}) {
+							count++
+						}
+					}
+				}
+			}
+		}
+	}
+	fmt.Println(count)
+}
+
+func findXMas(m map[P]byte, start, delta P) bool {
+	return m[start] == 'X' &&
+		m[start.Add(delta, 1)] == 'M' &&
+		m[start.Add(delta, 2)] == 'A' &&
+		m[start.Add(delta, 3)] == 'S'
+}

2024/4/main2.go

@@ -0,0 +1,30 @@
+package main
+
+import "fmt"
+
+func main() {
+	m := input()
+
+	count := 0
+	for x := 0; x < Size; x++ {
+		for y := 0; y < Size; y++ {
+			if findCrossMas(m, P{x, y}) {
+				count++
+			}
+		}
+	}
+	fmt.Println(count)
+}
+
+func findCrossMas(m map[P]byte, start P) bool {
+	if m[start] != 'A' {
+		return false
+	}
+	s := string([]byte{
+		m[P{start.x - 1, start.y - 1}],
+		m[P{start.x - 1, start.y + 1}],
+		m[P{start.x + 1, start.y + 1}],
+		m[P{start.x + 1, start.y - 1}],
+	})
+	return s == "MMSS" || s == "MSSM" || s == "SSMM" || s == "SMMS"
+}