day12

day12p1/solution.go

@@ -0,0 +1,63 @@
+package day12p1
+
+import (
+	"io"
+
+	"aoc/utils"
+)
+
+type position struct {
+	x, y int
+}
+
+func Solve(r io.Reader) any {
+	lines := utils.ReadLines(r)
+	board := make([][]rune, len(lines))
+	for i, line := range lines {
+		board[i] = []rune(line)
+	}
+
+	sum := 0
+	checked := make(map[position]bool)
+
+	for y := 0; y < len(board); y++ {
+		for x := 0; x < len(board[y]); x++ {
+			pos := position{x, y}
+			if checked[pos] {
+				continue
+			}
+			numChecked := len(checked)
+			perimeter := makeRegion(board, pos, checked)
+			area := len(checked) - numChecked
+
+			sum += area * perimeter
+		}
+	}
+
+	return sum
+}
+
+func makeRegion(board [][]rune, pos position, checked map[position]bool) int {
+	perimeter := 0
+	rtype := board[pos.y][pos.x]
+	expandArea(board, pos, rtype, checked, &perimeter)
+	return perimeter
+}
+
+func expandArea(board [][]rune, pos position, rtype rune, checked map[position]bool, perimeter *int) {
+	if oob(board, pos) || board[pos.y][pos.x] != rtype {
+		*perimeter++
+		return
+	}
+	if checked[pos] {
+		return
+	}
+	checked[pos] = true
+	for _, dir := range []position{{0, 1}, {0, -1}, {1, 0}, {-1, 0}} {
+		expandArea(board, position{pos.x + dir.x, pos.y + dir.y}, rtype, checked, perimeter)
+	}
+}
+
+func oob(board [][]rune, pos position) bool {
+	return pos.y < 0 || pos.y >= len(board) || pos.x < 0 || pos.x >= len(board[pos.y])
+}

day12p1/solution_test.go

@@ -0,0 +1,42 @@
+package day12p1
+
+import (
+	"strings"
+	"testing"
+
+	"aoc/utils"
+)
+
+var testInput = `RRRRIICCFF
+RRRRIICCCF
+VVRRRCCFFF
+VVRCCCJFFF
+VVVVCJJCFE
+VVIVCCJJEE
+VVIIICJJEE
+MIIIIIJJEE
+MIIISIJEEE
+MMMISSJEEE`
+
+func TestSolve(t *testing.T) {
+	tests := []struct {
+		input  string
+		answer int
+	}{
+		{testInput, 1930},
+	}
+
+	if testing.Verbose() {
+		utils.Verbose = true
+	}
+
+	for _, test := range tests {
+		r := strings.NewReader(test.input)
+
+		result := Solve(r).(int)
+
+		if result != test.answer {
+			t.Errorf("Expected %d, got %d", test.answer, result)
+		}
+	}
+}

day12p2/solution.go

@@ -0,0 +1,87 @@
+package day12p2
+
+import (
+	"io"
+	"slices"
+
+	"aoc/utils"
+)
+
+type position struct {
+	x, y int
+}
+
+func Solve(r io.Reader) any {
+	lines := utils.ReadLines(r)
+	board := make([][]rune, len(lines))
+	for i, line := range lines {
+		board[i] = []rune(line)
+	}
+
+	sum := 0
+	checked := make(map[position]bool)
+
+	for y := 0; y < len(board); y++ {
+		for x := 0; x < len(board[y]); x++ {
+			pos := position{x, y}
+			if checked[pos] {
+				continue
+			}
+			numChecked := len(checked)
+			sides := makeRegion(board, pos, checked)
+			area := len(checked) - numChecked
+
+			sum += area * sides
+		}
+	}
+
+	return sum
+}
+
+func makeRegion(board [][]rune, pos position, checked map[position]bool) int {
+	sides := 0
+	region := make(map[position]bool)
+	rtype := board[pos.y][pos.x]
+	expandArea(board, pos, rtype, checked, region)
+	outDirections := make(map[position][]position)
+	for row := range board {
+		for col := range board[row] {
+			if !region[position{col, row}] {
+				continue
+			}
+			for _, dir := range []position{{0, 1}, {1, 0}, {0, -1}, {-1, 0}} {
+				newPos := position{col + dir.x, row + dir.y}
+				if !oob(board, newPos) && board[newPos.y][newPos.x] == rtype {
+					continue
+				}
+				leftDir := position{dir.y, -dir.x}
+				left := position{col + leftDir.x, row + leftDir.y}
+				rightDir := position{-dir.y, dir.x}
+				right := position{col + rightDir.x, row + rightDir.y}
+				if !slices.Contains(outDirections[left], dir) && !slices.Contains(outDirections[right], dir) {
+					sides++
+				}
+				outDirections[position{col, row}] = append(outDirections[position{col, row}], dir)
+			}
+		}
+	}
+	return sides
+}
+
+func expandArea(board [][]rune, pos position, rtype rune, checked map[position]bool, region map[position]bool) {
+	if oob(board, pos) || board[pos.y][pos.x] != rtype {
+		return
+	}
+	if checked[pos] {
+		return
+	}
+	region[pos] = true
+	checked[pos] = true
+	for _, dir := range []position{{0, 1}, {0, -1}, {1, 0}, {-1, 0}} {
+		expandArea(board, position{pos.x + dir.x, pos.y + dir.y}, rtype, checked, region)
+	}
+}
+
+func oob(board [][]rune, pos position) bool {
+	return pos.y < 0 || pos.y >= len(board) || pos.x < 0 || pos.x >= len(board[pos.y])
+}

day12p2/solution_test.go

@@ -0,0 +1,42 @@
+package day12p2
+
+import (
+	"strings"
+	"testing"
+
+	"aoc/utils"
+)
+
+var testInput = `RRRRIICCFF
+RRRRIICCCF
+VVRRRCCFFF
+VVRCCCJFFF
+VVVVCJJCFE
+VVIVCCJJEE
+VVIIICJJEE
+MIIIIIJJEE
+MIIISIJEEE
+MMMISSJEEE`
+
+func TestSolve(t *testing.T) {
+	tests := []struct {
+		input  string
+		answer int
+	}{
+		{testInput, 1206},
+	}
+
+	if testing.Verbose() {
+		utils.Verbose = true
+	}
+
+	for _, test := range tests {
+		r := strings.NewReader(test.input)
+
+		result := Solve(r).(int)
+
+		if result != test.answer {
+			t.Errorf("Expected %d, got %d", test.answer, result)
+		}
+	}
+}