day04

2025/go/day04/day04.go

@@ -0,0 +1,92 @@
+package day04
+
+import (
+	"adventofcode2025/utils/grid2d"
+	"adventofcode2025/utils/inputs"
+)
+
+func Part1(input string) int {
+	adj := 0
+	rolls := 0
+	grid := inputs.ToGrid2D(input, "\n", "", "", func(c string) string { return c })
+	directions := [][]int{{0, 1}, {0, -1}, {1, 0}, {-1, 0}, {-1, 1}, {1, 1}, {-1, -1}, {1, -1}}
+	for j := 0; j < grid.SizeY(); j++ {
+		for i := 0; i < grid.SizeX(); i++ {
+			if !checkChar(i, j, grid, "@") {
+				continue
+			}
+			for _, dir := range directions {
+				x := i + dir[0]
+				y := j + dir[1]
+				if checkChar(x, y, grid, "@") {
+					adj++
+				}
+			}
+			if adj < 4 {
+				rolls++
+			}
+			adj = 0
+		}
+	}
+	return rolls
+}
+
+func Part2(input string) int {
+	grid := inputs.ToGrid2D(input, "\n", "", "", func(c string) string { return c })
+	rolls := countRolls(grid)
+	total := rolls
+
+	for rolls > 0 {
+		removeRolls(grid)        // modifies grid
+		rolls = countRolls(grid) // compute only once per loop
+		total += rolls
+	}
+
+	return total
+}
+
+func checkChar(x int, y int, grid *grid2d.Grid[string], c string) bool {
+	if x < 0 || x >= grid.SizeX() || y < 0 || y >= grid.SizeY() {
+		return false
+	}
+	if grid.Get(x, y) == c {
+		return true
+	}
+	return false
+}
+
+func countRolls(grid *grid2d.Grid[string]) int {
+	adj := 0
+	rolls := 0
+	directions := [][]int{{0, 1}, {0, -1}, {1, 0}, {-1, 0}, {-1, 1}, {1, 1}, {-1, -1}, {1, -1}}
+	for j := 0; j < grid.SizeY(); j++ {
+		for i := 0; i < grid.SizeX(); i++ {
+			if checkChar(i, j, grid, ".") {
+				continue
+			}
+			for _, dir := range directions {
+				x := i + dir[0]
+				y := j + dir[1]
+				if checkChar(x, y, grid, "@") || checkChar(x, y, grid, "x") {
+					adj++
+				}
+			}
+			if adj < 4 {
+				grid.Set(i, j, "x")
+				rolls++
+			}
+			adj = 0
+		}
+	}
+	return rolls
+}
+func removeRolls(grid *grid2d.Grid[string]) {
+	for j := 0; j < grid.SizeY(); j++ {
+		for i := 0; i < grid.SizeX(); i++ {
+			if checkChar(i, j, grid, "x") {
+				grid.Set(i, j, ".")
+			}
+		}
+	}
+
+}