Day 23, 2022

go/2022/day23/input.txt

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go/2022/day23/main.go

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+package main
+
+import (
+	_ "embed"
+	"fmt"
+	"github.com/yeurch/advent-of-code/go/ysl"
+	"math"
+	"strings"
+	"time"
+)
+
+//go:embed input.txt
+var inputDay string
+
+type Point struct {
+	x int
+	y int
+}
+
+func (p *Point) Add(other Point) Point {
+	return Point{p.x + other.x, p.y + other.y}
+}
+
+type Rule struct {
+	direction  Point
+	ifAllEmpty []Point
+}
+
+var rule0 = Rule{Point{0, 0}, []Point{
+	{-1, -1}, {0, -1}, {1, -1},
+	{-1, 0}, {1, 0},
+	{-1, 1}, {0, 1}, {1, 1},
+}}
+var rules = []Rule{
+	{Point{0, 1}, []Point{{-1, 1}, {0, 1}, {1, 1}}},
+	{Point{0, -1}, []Point{{-1, -1}, {0, -1}, {1, -1}}},
+	{Point{-1, 0}, []Point{{-1, -1}, {-1, 0}, {-1, 1}}},
+	{Point{1, 0}, []Point{{1, -1}, {1, 0}, {1, 1}}},
+}
+
+func Part1(input string) int {
+	elves := parseInput(input)
+
+	for i := 0; i < 10; i++ {
+		elves, _ = doMove(i, &elves)
+	}
+
+	return getNumEmpty(&elves)
+}
+func Part2(input string) int {
+	elves := parseInput(input)
+
+	i := 0
+	for {
+		var n int
+		elves, n = doMove(i, &elves)
+		if n == 0 {
+			break
+		}
+		i++
+	}
+
+	return i + 1
+}
+
+// Processes a move and returns the new positions of elves, along with the number of elves that moved
+func doMove(moveNum int, elves *[]Point) ([]Point, int) {
+	startPositions := ysl.NewSet[Point]()
+	for _, p := range *elves {
+		startPositions.Add(p)
+	}
+
+	// Determine intentions
+	numMoved := 0
+	intentions := append([]Point{}, *elves...) // Make a copy of elves, so each initial intention is to move nowhere
+	for j, p := range intentions {
+		if checkRule(&startPositions, &p, &rule0) {
+			continue // This elf won't move, as it has no neighbours
+		}
+		for ruleNum := 0; ruleNum < len(rules); ruleNum++ {
+			rule := rules[(moveNum+ruleNum)%len(rules)]
+			if checkRule(&startPositions, &p, &rule) {
+				intentions[j] = p.Add(rule.direction)
+				numMoved++
+				break
+			}
+		}
+
+	}
+
+	// Duplicate intention detection
+	dupes := ysl.NewSet[Point]()
+	intentionSet := ysl.NewSet[Point]()
+	for _, intention := range intentions {
+		ok := intentionSet.Add(intention)
+		if !ok {
+			dupes.Add(intention)
+		}
+	}
+
+	for i, p := range intentions {
+		if dupes.Contains(p) {
+			intentions[i] = (*elves)[i] // Cancel the intent of this elf
+			numMoved--
+		}
+	}
+
+	return intentions, numMoved
+}
+func checkRule(startPositions *ysl.Set[Point], p *Point, rule *Rule) bool {
+	for _, checkDir := range rule.ifAllEmpty {
+		if (*startPositions).Contains(p.Add(checkDir)) {
+			return false
+		}
+	}
+	return true
+}
+
+func parseInput(input string) []Point {
+	lines := strings.Split(strings.TrimSuffix(input, "\n"), "\n")
+
+	result := make([]Point, 0)
+	for i, line := range lines {
+		y := len(lines) - i - 1
+		for x, c := range line {
+			if c == '#' {
+				result = append(result, Point{x, y})
+			}
+		}
+	}
+
+	return result
+}
+
+func getBounds(elves *[]Point) [2]Point {
+	minX, maxX, minY, maxY := math.MaxInt, math.MinInt, math.MaxInt, math.MinInt
+	for _, p := range *elves {
+		if p.x < minX {
+			minX = p.x
+		}
+		if p.x > maxX {
+			maxX = p.x
+		}
+		if p.y < minY {
+			minY = p.y
+		}
+		if p.y > maxY {
+			maxY = p.y
+		}
+	}
+	var bounds [2]Point
+	bounds[0].x = minX
+	bounds[0].y = minY
+	bounds[1].x = maxX
+	bounds[1].y = maxY
+	return bounds
+}
+func getNumEmpty(elves *[]Point) int {
+	bounds := getBounds(elves)
+	area := (bounds[1].x - bounds[0].x + 1) * (bounds[1].y - bounds[0].y + 1)
+	return area - len(*elves)
+}
+
+func main() {
+	fmt.Println("*** Advent of Code 2022, day 23 ***")
+
+	start := time.Now()
+	fmt.Println("part1: ", Part1(inputDay))
+	fmt.Println(time.Since(start))
+
+	start = time.Now()
+	fmt.Println("part2: ", Part2(inputDay))
+	fmt.Println(time.Since(start))
+}