1 files changed, 181 insertions, 0 deletions
diff --git a/day12/main.go b/day12/main.go
new file mode 100644
index 0000000..60b0ecd
--- /dev/null
+++ b/day12/main.go
@@ -0,0 +1,181 @@
+package main
+
+import (
+	"bufio"
+	"fmt"
+	"os"
+	"strings"
+)
+
+func main() {
+	fmt.Println("Part 1")
+	fmt.Println(part1(readData("example1.txt")), 140)
+	fmt.Println(part1(readData("example2.txt")), 772)
+	fmt.Println(part1(readData("example3.txt")), 1930)
+	fmt.Println(part1(readData("data.txt")))
+	fmt.Println()
+	fmt.Println("Part 2")
+	fmt.Println(part2(readData("example1.txt")), 80)
+	fmt.Println(part2(readData("example2.txt")), 436)
+	fmt.Println(part2(readData("example3.txt")), 1206)
+	fmt.Println(part2(readData("example4.txt")), 236)
+	fmt.Println(part2(readData("example5.txt")), 368)
+	fmt.Println(part2(readData("data.txt")))
+}
+
+func part2(plots [][]byte) (totalPrice int) {
+	visited := make([][]int, len(plots))
+	for i, line := range plots {
+		visited[i] = make([]int, len(line))
+	}
+
+	nextPlotId := 1
+	areas := make([]int, 1)
+	for y := range len(plots) {
+		for x := range len(plots[y]) {
+			if visited[y][x] > 0 {
+				continue
+			}
+			area := visitPlot2(plots, visited, nextPlotId, x, y)
+			areas = append(areas, area)
+			nextPlotId += 1
+		}
+	}
+
+	sides := make([]int, len(areas))
+
+	for y := range len(plots) + 1 {
+		p0, p1 := 0, 0
+		for x := range len(plots[0]) + 1 {
+			p0Next := getPlotIdOrZero(visited, x, y-1)
+			p1Next := getPlotIdOrZero(visited, x, y)
+			scanSides(visited, sides, p0, p1, p0Next, p1Next)
+			p0, p1 = p0Next, p1Next
+		}
+	}
+
+	for x := range len(plots[0]) + 1 {
+		p0, p1 := 0, 0
+		for y := range len(plots) + 1 {
+			p0Next := getPlotIdOrZero(visited, x-1, y)
+			p1Next := getPlotIdOrZero(visited, x, y)
+			scanSides(visited, sides, p0, p1, p0Next, p1Next)
+			p0, p1 = p0Next, p1Next
+		}
+	}
+
+	for i := range areas {
+		totalPrice += areas[i] * sides[i]
+	}
+
+	return
+}
+
+func scanSides(visited [][]int, sides []int, p0, p1, p0Next, p1Next int) {
+	if p0Next != p1Next {
+		if p0 == p1 {
+			sides[p0Next] += 1
+			sides[p1Next] += 1
+		} else {
+			if p0 != p0Next {
+				sides[p0Next] += 1
+			}
+			if p1 != p1Next {
+				sides[p1Next] += 1
+			}
+		}
+	}
+}
+
+var DIR = [4][2]int{{0, -1}, {-1, 0}, {0, 1}, {1, 0}}
+
+func visitPlot2(plots [][]byte, visited [][]int, plotId int, x, y int) (area int) {
+	if visited[y][x] > 0 {
+		return
+	}
+
+	visited[y][x] = plotId
+	area += 1
+
+	p := plots[y][x]
+
+	for _, dir := range DIR {
+		other := getPlotOrZero(plots, x+dir[0], y+dir[1])
+		if other == p {
+			area += visitPlot2(plots, visited, plotId, x+dir[0], y+dir[1])
+		}
+	}
+
+	return
+}
+
+func getPlotOrZero(plots [][]byte, x, y int) byte {
+	if x < 0 || y < 0 || y >= len(plots) || x >= len(plots[y]) {
+		return 0
+	} else {
+		return plots[y][x]
+	}
+}
+
+func getPlotIdOrZero(plots [][]int, x, y int) int {
+	if x < 0 || y < 0 || y >= len(plots) || x >= len(plots[y]) {
+		return 0
+	} else {
+		return plots[y][x]
+	}
+}
+
+func part1(plots [][]byte) (totalPrice int) {
+	visited := make([][]bool, len(plots))
+	for i, line := range plots {
+		visited[i] = make([]bool, len(line))
+	}
+
+	for y := range len(plots) {
+		for x := range len(plots[y]) {
+			area, perimeter := visitPlot1(plots, visited, x, y)
+			totalPrice += area * perimeter
+		}
+	}
+
+	return
+}
+
+func visitPlot1(plots [][]byte, visited [][]bool, x, y int) (area, perimeter int) {
+	if visited[y][x] {
+		return
+	}
+
+	visited[y][x] = true
+	area += 1
+
+	p := plots[y][x]
+
+	for _, dir := range DIR {
+		other := getPlotOrZero(plots, x+dir[0], y+dir[1])
+
+		if other == p {
+			otherArea, otherPerimeter := visitPlot1(plots, visited, x+dir[0], y+dir[1])
+			area += otherArea
+			perimeter += otherPerimeter
+		} else {
+			perimeter += 1
+		}
+	}
+
+	return
+}
+
+func readData(fileName string) (plots [][]byte) {
+	fp, err := os.Open(fileName)
+	if err != nil {
+		panic(err)
+	}
+
+	scanner := bufio.NewScanner(fp)
+	for scanner.Scan() {
+		line := strings.TrimSpace(scanner.Text())
+		plots = append(plots, []byte(line))
+	}
+	return
+}