refactor: extract region logic into separate package

cmd/12/main.go

@@ -2,10 +2,9 @@ package main
 
 import (
 	"regexp"
-	"sort"
-	"strconv"
 	"strings"
 
+	"github.com/StevanFreeborn/advent-of-code-2025/cmd/12/region"
 	"github.com/StevanFreeborn/advent-of-code-2025/cmd/12/shape"
 	"github.com/StevanFreeborn/advent-of-code-2025/internal/file"
 )
@@ -22,7 +21,7 @@ func SolvePartOne(filePath string) int {
 
 	total := 0
 	shapes := map[int][]shape.Shape{}
-	regions := []string{}
+	regions := []region.Region{}
 
 	for _, section := range sections {
 		lines := newLineRegex.Split(strings.TrimSpace(section), -1)
@@ -36,129 +35,16 @@ func SolvePartOne(filePath string) int {
 
 		for _, line := range lines {
 			if strings.Contains(line, COLON) {
-				regions = append(regions, line)
+				regions = append(regions, region.From(line))
 			}
 		}
 	}
 
 	for _, region := range regions {
-		parts := strings.Split(region, COLON)
+		if region.CanFit(shapes) {
-		dims := strings.Split(parts[0], X)
-		width, _ := strconv.Atoi(dims[0])
-		height, _ := strconv.Atoi(dims[1])
-
-		countsStr := strings.Fields(parts[1])
-		requiredShapes := []int{}
-
-		for id, s := range countsStr {
-			count, _ := strconv.Atoi(s)
-
-			for range count {
-				requiredShapes = append(requiredShapes, id)
-			}
-		}
-
-		if canFit(width, height, requiredShapes, shapes) {
 			total++
 		}
 	}
 
 	return total
 }
-
-type item struct {
-	id       int
-	area     int
-	variants []shape.Shape
-}
-
-func canFit(width int, height int, requiredShapes []int, shapes map[int][]shape.Shape) bool {
-	totalArea := 0
-
-	itemsToPlace := make([]item, 0, len(requiredShapes))
-
-	for _, id := range requiredShapes {
-		shapeVariants := shapes[id]
-		area := shapeVariants[0].Area()
-		totalArea += area
-		itemsToPlace = append(itemsToPlace, item{id: id, area: area, variants: shapeVariants})
-	}
-
-	if totalArea > width*height {
-		return false
-	}
-
-	sort.Slice(itemsToPlace, func(i, j int) bool {
-		return itemsToPlace[i].area > itemsToPlace[j].area
-	})
-
-	grid := make([][]bool, height)
-
-	for i := range grid {
-		grid[i] = make([]bool, width)
-	}
-
-	return checkFit(0, itemsToPlace, grid, width, height)
-}
-
-func checkFit(index int, itemsToPlace []item, grid [][]bool, width int, height int) bool {
-	if index == len(itemsToPlace) {
-		return true
-	}
-
-	itemToPlace := itemsToPlace[index]
-
-	for _, variant := range itemToPlace.variants {
-		maxRow := variant.MaxRow()
-		maxColumn := variant.MaxColumn()
-
-		lastRow := height - maxRow
-		lastColumn := width - maxColumn
-
-		for r := range lastRow {
-			for c := range lastColumn {
-				if canPlace(grid, r, c, variant) {
-					place(grid, r, c, variant)
-
-					if checkFit(index+1, itemsToPlace, grid, width, height) {
-						return true
-					}
-
-					unplace(grid, r, c, variant)
-				}
-			}
-		}
-	}
-
-	return false
-}
-
-func canPlace(grid [][]bool, r, c int, variant shape.Shape) bool {
-	for _, position := range variant.Positions() {
-		absoluteRow := r + position.Row()
-		absoluteColumn := c + position.Column()
-		isOccupied := grid[absoluteRow][absoluteColumn]
-
-		if isOccupied {
-			return false
-		}
-	}
-
-	return true
-}
-
-func place(grid [][]bool, r, c int, variant shape.Shape) {
-	for _, position := range variant.Positions() {
-		absoluteRow := r + position.Row()
-		absoluteColumn := c + position.Column()
-		grid[absoluteRow][absoluteColumn] = true
-	}
-}
-
-func unplace(grid [][]bool, r, c int, variant shape.Shape) {
-	for _, position := range variant.Positions() {
-		absoluteRow := r + position.Row()
-		absoluteColumn := c + position.Column()
-		grid[absoluteRow][absoluteColumn] = false
-	}
-}

cmd/12/region/region.go

@@ -0,0 +1,158 @@
+// Package region provides a model and methods for manipulating a region
+package region
+
+import (
+	"sort"
+	"strconv"
+	"strings"
+
+	"github.com/StevanFreeborn/advent-of-code-2025/cmd/12/shape"
+)
+
+type Region interface {
+	CanFit(shapes map[int][]shape.Shape) bool
+}
+
+type region struct {
+	width          int
+	height         int
+	requiredShapes []int
+}
+
+func From(line string) Region {
+	parts := strings.Split(line, ":")
+	dims := strings.Split(parts[0], "x")
+	width, _ := strconv.Atoi(dims[0])
+	height, _ := strconv.Atoi(dims[1])
+
+	countsStr := strings.Fields(parts[1])
+	requiredShapes := []int{}
+
+	for id, s := range countsStr {
+		count, _ := strconv.Atoi(s)
+
+		for range count {
+			requiredShapes = append(requiredShapes, id)
+		}
+	}
+
+	return region{
+		width:          width,
+		height:         height,
+		requiredShapes: requiredShapes,
+	}
+}
+
+func (r region) CanFit(shapes map[int][]shape.Shape) bool {
+	totalArea := 0
+
+	itemsToPlace := r.createItems(shapes)
+
+	for _, item := range itemsToPlace {
+		totalArea += item.area
+	}
+
+	if totalArea > r.area() {
+		return false
+	}
+
+	return r.checkFit(0, itemsToPlace, r.createGrid())
+}
+
+type item struct {
+	id       int
+	area     int
+	variants []shape.Shape
+}
+
+func (r region) checkFit(index int, itemsToPlace []item, grid [][]bool) bool {
+	if index == len(itemsToPlace) {
+		return true
+	}
+
+	currentItem := itemsToPlace[index]
+
+	for _, variant := range currentItem.variants {
+		maxRow := variant.MaxRow()
+		maxColumn := variant.MaxColumn()
+
+		lastRow := r.height - maxRow
+		lastColumn := r.width - maxColumn
+
+		for rowNumber := range lastRow {
+			for columnNumber := range lastColumn {
+				if canPlace(grid, rowNumber, columnNumber, variant) {
+					place(grid, rowNumber, columnNumber, variant)
+
+					if r.checkFit(index+1, itemsToPlace, grid) {
+						return true
+					}
+
+					unplace(grid, rowNumber, columnNumber, variant)
+				}
+			}
+		}
+	}
+
+	return false
+}
+
+func (r region) area() int {
+	return r.width * r.height
+}
+
+func (r region) createGrid() [][]bool {
+	grid := make([][]bool, r.height)
+
+	for i := range grid {
+		grid[i] = make([]bool, r.width)
+	}
+
+	return grid
+}
+
+func (r region) createItems(shapes map[int][]shape.Shape) []item {
+	itemsToPlace := make([]item, 0, len(r.requiredShapes))
+
+	for _, id := range r.requiredShapes {
+		shapeVariants := shapes[id]
+		area := shapeVariants[0].Area()
+		itemsToPlace = append(itemsToPlace, item{id: id, area: area, variants: shapeVariants})
+	}
+
+	sort.Slice(itemsToPlace, func(i, j int) bool {
+		return itemsToPlace[i].area > itemsToPlace[j].area
+	})
+
+	return itemsToPlace
+}
+
+func canPlace(grid [][]bool, r, c int, variant shape.Shape) bool {
+	for _, position := range variant.Positions() {
+		absoluteRow := r + position.Row()
+		absoluteColumn := c + position.Column()
+		isOccupied := grid[absoluteRow][absoluteColumn]
+
+		if isOccupied {
+			return false
+		}
+	}
+
+	return true
+}
+
+func place(grid [][]bool, r, c int, variant shape.Shape) {
+	for _, position := range variant.Positions() {
+		absoluteRow := r + position.Row()
+		absoluteColumn := c + position.Column()
+		grid[absoluteRow][absoluteColumn] = true
+	}
+}
+
+func unplace(grid [][]bool, r, c int, variant shape.Shape) {
+	for _, position := range variant.Positions() {
+		absoluteRow := r + position.Row()
+		absoluteColumn := c + position.Column()
+		grid[absoluteRow][absoluteColumn] = false
+	}
+}