2024 Day 4 Complete!

2024/day04/main.go

@@ -0,0 +1,85 @@
+package main
+
+import (
+	"fmt"
+
+	h "git.bullercodeworks.com/brian/adventofcode/helpers"
+)
+
+func main() {
+	inp := h.StdinToCoordMap()
+	part1(inp)
+	part2(inp)
+}
+
+func part1(m h.CoordByteMap) {
+	var total int
+	for y := m.TLY; y <= m.BRY; y++ {
+		for x := m.TLX; x <= m.BRX; x++ {
+			total += checkPos(m, h.Coordinate{X: x, Y: y})
+		}
+	}
+	fmt.Println("# Part 1")
+	fmt.Println("Instances of XMAS:", total)
+}
+
+func part2(m h.CoordByteMap) {
+	var total int
+	for y := m.TLY; y <= m.BRY; y++ {
+		for x := m.TLX; x <= m.BRX; x++ {
+			if checkXPos(m, h.Coordinate{X: x, Y: y}) {
+				total++
+			}
+		}
+	}
+	fmt.Println("# Part 2")
+	fmt.Println("Instances of X-MAS:", total)
+}
+
+// checkPos takes an x,y and returns how many instances of
+// 'XMAS' occur starting there.
+func checkPos(m h.CoordByteMap, c h.Coordinate) int {
+	if m.Get(c) != 'X' {
+		return 0
+	}
+
+	var total int
+	for _, dir := range []h.Coordinate{
+		{X: -1, Y: 0},  // North
+		{X: -1, Y: 1},  // Northeast
+		{X: 0, Y: 1},   // East
+		{X: 1, Y: 1},   // Southeast
+		{X: 1, Y: 0},   // South
+		{X: 1, Y: -1},  // Southwest
+		{X: 0, Y: -1},  // West
+		{X: -1, Y: -1}, // Northwest
+	} {
+		if checkDir(m, c, dir, []byte{'X', 'M', 'A', 'S'}) {
+			total++
+		}
+	}
+	return total
+}
+
+// checkDir follows a direction to look for the word returning true if found.
+func checkDir(m h.CoordByteMap, c h.Coordinate, dir h.Coordinate, word []byte) bool {
+	if len(word) == 0 {
+		return true
+	}
+	if m.Get(c) != word[0] {
+		return false
+	}
+	return checkDir(m, c.Relative(dir), dir, word[1:])
+}
+
+func checkXPos(m h.CoordByteMap, c h.Coordinate) bool {
+	if m.Get(c) != 'A' {
+		return false
+	}
+	// A X-Mas can be:
+	// M S  S M  M M  S S
+	//  A    A    A    A
+	// M S  S M  S S  M M
+	wrk := string([]byte{m.Get(c.NE()), m.Get(c.SW()), m.Get(c.NW()), m.Get(c.SE())})
+	return wrk == "MSMS" || wrk == "SMSM" || wrk == "MSSM" || wrk == "SMMS"
+}