Add solution day 12 part 1

Author: terminalnode

.gitignore

@@ -1,3 +1,5 @@
+main
+
 input/*
 !input/.gitkeep
 

README.md

@@ -56,5 +56,5 @@ automatically rebuilt and redeployed ever time the `common` module or their own
 | 09  |          | 22  |          |
 | 10  | ⭐ ⭐      | 23  |          |
 | 11  | ⭐ ⭐      | 24  |          |
-| 12  |          | 25  |          |
+| 12  | ⭐        | 25  |          |
 | 13  |          |     |          |

main

@@ -1,9 +1,189 @@
 package main
 
 import (
+	"fmt"
 	"github.com/terminalnode/adventofcode2024/common"
+	"github.com/terminalnode/adventofcode2024/common/util"
+	"log"
+	"strings"
 )
 
+type plotMap = [][]plot
+type plot struct {
+	Label int
+	Hash  string
+}
+
 func main() {
-	common.Setup(12, nil, nil)
+	common.Setup(12, part1, nil)
+}
+
+func part1(
+	input string,
+) string {
+	sum := 0
+	fields := 0
+	plots := parsePlots(input)
+	visited := make(map[string]bool)
+
+	rows := len(plots)
+	for y := 0; y < rows; y++ {
+		columns := len(plots[y])
+		for x := 0; x < columns; x++ {
+			c := util.Coordinate{X: x, Y: y}
+			area, perimeter, _ := countField(plots, c, visited)
+			sum += area * perimeter
+
+			if area != 0 {
+				label := plots[y][x].Label
+				log.Printf("Field %c at (%d,%d), area=%d, perim=%d", label, x, y, area, perimeter)
+				fields++
+			}
+		}
+	}
+
+	return fmt.Sprintf("Area * perimeter of %d fields: %d", fields, sum)
+}
+
+func part2(
+	input string,
+) string {
+	sum := 0
+	fields := 0
+	plots := parsePlots(input)
+	visited := make(map[string]bool)
+
+	rows := len(plots)
+	for y := 0; y < rows; y++ {
+		columns := len(plots[y])
+		for x := 0; x < columns; x++ {
+			c := util.Coordinate{X: x, Y: y}
+			area, _, corners := countField(plots, c, visited)
+			sum += area * corners
+
+			if area != 0 {
+				label := plots[y][x].Label
+				log.Printf("Field %c at (%d,%d), area=%d, corners=%d", label, x, y, area, corners)
+				fields++
+			}
+		}
+	}
+
+	return fmt.Sprintf("Area * sides of %d fields: %d", fields, sum)
+}
+
+func parsePlots(
+	input string,
+) plotMap {
+	lines := strings.Split(input, "\n")
+	m := make([][]plot, len(lines))
+
+	for y, row := range lines {
+		m[y] = make([]plot, len(row))
+		for x, char := range row {
+			c := util.Coordinate{X: x, Y: y}
+			p := plot{Label: int(char), Hash: c.String()}
+			m[y][x] = p
+		}
+	}
+
+	return m
+}
+
+func countField(
+	plots plotMap,
+	c util.Coordinate,
+	visited map[string]bool,
+) (int, int, int) {
+	if visited[c.String()] {
+		return 0, 0, 0
+	}
+	visited[c.String()] = true
+
+	area := 1
+	perimeter := 0
+
+	n := c.North()
+	e := c.East()
+	s := c.South()
+	w := c.West()
+
+	label := plots[c.Y][c.X].Label
+	nSame := isSameField(plots, label, n)
+	eSame := isSameField(plots, label, e)
+	sSame := isSameField(plots, label, s)
+	wSame := isSameField(plots, label, w)
+	corners := countCorners(nSame, eSame, sSame, wSame)
+
+	if nSame {
+		a, p, c := countField(plots, n, visited)
+		area += a
+		perimeter += p
+		corners += c
+	} else {
+		perimeter++
+	}
+
+	if eSame {
+		a, p, c := countField(plots, e, visited)
+		area += a
+		perimeter += p
+		corners += c
+	} else {
+		perimeter++
+	}
+
+	if sSame {
+		a, p, c := countField(plots, s, visited)
+		area += a
+		perimeter += p
+		corners += c
+	} else {
+		perimeter++
+	}
+
+	if wSame {
+		a, p, c := countField(plots, w, visited)
+		area += a
+		perimeter += p
+		corners += c
+	} else {
+		perimeter++
+	}
+
+	return area, perimeter, corners
+}
+
+func isSameField(
+	plots plotMap,
+	label int,
+	c util.Coordinate,
+) bool {
+	if !util.In2DArray(c, plots) {
+		return false
+	}
+	cell := plots[c.Y][c.X]
+	return cell.Label == label
+}
+
+func countCorners(
+	nSame bool,
+	eSame bool,
+	sSame bool,
+	wSame bool,
+) int {
+	sum := 0
+	if !nSame && !eSame {
+		sum++
+	}
+	if !nSame && !wSame {
+		sum++
+	}
+	if !sSame && !eSame {
+		sum++
+	}
+	if !sSame && !wSame {
+		sum++
+	}
+	return sum
 }