Day 09

cmd/aoc2021/register.go

@@ -11,6 +11,7 @@ import (
 	"github.com/yitsushi/advent-of-code-2021/days/day06"
 	"github.com/yitsushi/advent-of-code-2021/days/day07"
 	"github.com/yitsushi/advent-of-code-2021/days/day08"
+	"github.com/yitsushi/advent-of-code-2021/days/day09"
 )
 
 func withDays(month puzzle.Month) puzzle.Month {
@@ -22,6 +23,7 @@ func withDays(month puzzle.Month) puzzle.Month {
 	month.Register(6, &day06.Solver{})
 	month.Register(7, &day07.Solver{})
 	month.Register(8, &day08.Solver{})
+	month.Register(9, &day09.Solver{})
 
 	return month
 }

days/day09/error.go

@@ -0,0 +1,12 @@
+package day09
+
+import "fmt"
+
+// OutOfBoundError happens when we want to reach a position ouside of the map.
+type OutOfBoundError struct {
+	Index int
+}
+
+func (e OutOfBoundError) Error() string {
+	return fmt.Sprintf("out of bound error: %d", e.Index)
+}

days/day09/fixtures/example

@@ -0,0 +1,5 @@
+2199943210
+3987894921
+9856789892
+8767896789
+9899965678

days/day09/fixtures/input

@@ -0,0 +1,100 @@
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days/day09/input.go

@@ -0,0 +1,34 @@
+package day09
+
+import (
+	"bufio"
+	"io"
+)
+
+// Solver is the main solver.
+type Solver struct {
+	input CaveMap
+}
+
+const (
+	asciiShift = 48
+)
+
+// SetInput receives the input and parses its content.
+func (d *Solver) SetInput(input io.Reader) error {
+	scanner := bufio.NewScanner(input)
+	d.input = newCaveMap()
+
+	for scanner.Scan() {
+		text := scanner.Text()
+		line := []int{}
+
+		for _, character := range text {
+			line = append(line, int(character-asciiShift))
+		}
+
+		d.input.AddLayer(line)
+	}
+
+	return nil
+}

days/day09/input_test.go

@@ -0,0 +1,23 @@
+package day09_test
+
+import (
+	"bytes"
+	"io/ioutil"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/yitsushi/advent-of-code-2021/days/day09"
+	test "github.com/yitsushi/go-aoc/testing"
+)
+
+func TestSolver_SetInput(t *testing.T) {
+	example, err := test.LoadFixture("example")
+	if !assert.NoError(t, err) {
+		return
+	}
+
+	day := day09.Solver{}
+	err = day.SetInput(ioutil.NopCloser(bytes.NewReader(example)))
+
+	assert.NoError(t, err)
+}

days/day09/main.go

@@ -0,0 +1,60 @@
+package day09
+
+import (
+	"fmt"
+	"sort"
+
+	"github.com/yitsushi/go-aoc/math"
+	"github.com/yitsushi/go-aoc/perf"
+)
+
+// Part1 for this day.
+func (d *Solver) Part1() (string, error) {
+	defer perf.Duration(perf.Track("Part1"))
+
+	result := 0
+
+	for _, location := range d.input.FindLowPoints() {
+		if value, err := d.input.Position(location); err == nil {
+			result += value + 1
+		}
+	}
+
+	return fmt.Sprintf("%d", result), nil
+}
+
+// Part2 for this day.
+func (d *Solver) Part2() (string, error) {
+	defer perf.Duration(perf.Track("Part2"))
+
+	basinSizes := []int{}
+
+	for _, sink := range d.input.FindLowPoints() {
+		basin := append(d.input.WhoCanFlowHere(sink), sink)
+		basinSizes = append(basinSizes, len(removeDuplicateValues(basin)))
+	}
+
+	sort.Slice(basinSizes, func(i, j int) bool {
+		return basinSizes[i] > basinSizes[j]
+	})
+
+	result := basinSizes[0] * basinSizes[1] * basinSizes[2]
+
+	return fmt.Sprintf("%d", result), nil
+}
+
+func removeDuplicateValues(input []math.Vector2DInt) []math.Vector2DInt {
+	keys := make(map[interface{}]bool)
+	list := []math.Vector2DInt{}
+
+	for _, entry := range input {
+		hash := entry.Hash()
+		if _, value := keys[hash]; !value {
+			keys[hash] = true
+
+			list = append(list, entry)
+		}
+	}
+
+	return list
+}

days/day09/map.go

@@ -0,0 +1,142 @@
+package day09
+
+import (
+	"github.com/yitsushi/go-aoc/math"
+)
+
+const (
+	topValue = 9
+)
+
+// CaveMap is the map of the cave.
+type CaveMap struct {
+	layers [][]int
+}
+
+func newCaveMap() CaveMap {
+	return CaveMap{layers: [][]int{}}
+}
+
+// AddLayer to the map.
+func (c *CaveMap) AddLayer(line []int) {
+	c.layers = append(c.layers, line)
+}
+
+// Layers of the map.
+func (c CaveMap) Layers() [][]int {
+	return c.layers
+}
+
+// Layer of the map.
+func (c CaveMap) Layer(n int) ([]int, error) {
+	if n < 0 || n >= len(c.layers) {
+		return []int{}, OutOfBoundError{Index: n}
+	}
+
+	return c.layers[n], nil
+}
+
+// Position value on the map.
+func (c CaveMap) Position(coord math.Vector2DInt) (int, error) {
+	targetRow, err := c.Layer(coord.Y)
+	if err != nil {
+		return -1, err
+	}
+
+	if coord.X < 0 || coord.X >= len(targetRow) {
+		return -1, OutOfBoundError{Index: coord.X}
+	}
+
+	return targetRow[coord.X], nil
+}
+
+// Adjacents positions.
+func (c CaveMap) Adjacents(coord math.Vector2DInt) []math.Vector2DInt {
+	result := []math.Vector2DInt{}
+
+	targets := []math.Vector2DInt{
+		{X: 0, Y: 1},
+		{X: 0, Y: -1},
+		{X: 1, Y: 0},
+		{X: -1, Y: 0},
+	}
+
+	for _, target := range targets {
+		if _, err := c.Position(coord.Add(target)); err == nil {
+			result = append(result, coord.Add(target))
+		}
+	}
+
+	return result
+}
+
+// IsLowest checks if all adjacents are higher or not.
+func (c CaveMap) IsLowest(coord math.Vector2DInt) bool {
+	value, err := c.Position(coord)
+	if err != nil {
+		return false
+	}
+
+	for _, adjacent := range c.Adjacents(coord) {
+		adjacentValue, err := c.Position(adjacent)
+		if err != nil {
+			continue
+		}
+
+		if adjacentValue <= value {
+			return false
+		}
+	}
+
+	return true
+}
+
+// FindLowPoints returns with all the positions where it's the lowest based
+// on its adjacent positions.
+func (c CaveMap) FindLowPoints() []math.Vector2DInt {
+	result := []math.Vector2DInt{}
+
+	for idy, line := range c.Layers() {
+		for idx := range line {
+			if c.IsLowest(math.Vector2DInt{Y: idy, X: idx}) {
+				result = append(
+					result,
+					math.Vector2DInt{X: idx, Y: idy},
+				)
+			}
+		}
+	}
+
+	return result
+}
+
+// WhoCanFlowHere walks up on the map from a point to discover basins.
+func (c CaveMap) WhoCanFlowHere(coord math.Vector2DInt) []math.Vector2DInt {
+	result := []math.Vector2DInt{}
+
+	value, err := c.Position(coord)
+	if err != nil {
+		return result
+	}
+
+	for _, target := range c.Adjacents(coord) {
+		targetValue, err := c.Position(target)
+		if err != nil {
+			continue
+		}
+
+		if targetValue == topValue {
+			continue
+		}
+
+		if targetValue > value {
+			result = append(result, target)
+		}
+	}
+
+	for _, target := range result {
+		result = append(result, c.WhoCanFlowHere(target)...)
+	}
+
+	return result
+}