2021 Day 20 Complete

2021/day20/main.go

@@ -0,0 +1,55 @@
+package main
+
+import (
+	"fmt"
+
+	h "git.bullercodeworks.com/brian/adventofcode/helpers"
+)
+
+func main() {
+	inp := h.StdinToStringSlice()
+	enhancement, inputImage := inp[0], h.StringSliceToCoordByteMap(inp[2:])
+	fmt.Println("# Part 1")
+	run(inputImage, enhancement, 2)
+	fmt.Println()
+	fmt.Println("# Part 2")
+	run(inputImage, enhancement, 50)
+}
+
+func run(image h.CoordByteMap, enhancement string, iters int) {
+	bg := byte('.')
+	for i := 0; i < iters; i++ {
+		image = enhance(image, enhancement, bg)
+		if bg == '#' {
+			bg = enhancement[511]
+		} else {
+			bg = enhancement[0]
+		}
+	}
+	fmt.Println("Lit pixels:", image.Count('#'))
+}
+
+func enhance(image h.CoordByteMap, enhancement string, bg byte) h.CoordByteMap {
+	pxToInt := func(c h.Coordinate) int {
+		var num int
+		for bldY := c.Y - 1; bldY <= c.Y+1; bldY++ {
+			for bldX := c.X - 1; bldX <= c.X+1; bldX++ {
+				num = num << 1
+				v := image.Opt(h.Coordinate{X: bldX, Y: bldY}, bg)
+				if v == '#' {
+					num |= 1
+				}
+			}
+		}
+		return num
+	}
+	next := h.NewCoordByteMap()
+	for y := image.TLY - 1; y <= image.BRY+1; y++ {
+		for x := image.TLX - 1; x <= image.BRX+1; x++ {
+			c := h.Coordinate{X: x, Y: y}
+			nv := enhancement[pxToInt(c)]
+			next.Put(c, nv)
+		}
+	}
+	return next
+}