2018 day23 crazy shrinking box solution, kind of a binary search

2018/day23/main.go

@@ -0,0 +1,147 @@
+package main
+
+import (
+	"flag"
+	"fmt"
+	"math"
+	"strings"
+
+	"github.com/alexchao26/advent-of-code-go/util"
+)
+
+func main() {
+	var part int
+	flag.IntVar(&part, "part", 1, "part 1 or 2")
+	flag.Parse()
+	fmt.Println("Running part", part)
+
+	if part == 1 {
+		ans := part1(util.ReadFile("./input.txt"))
+		fmt.Println("Output:", ans)
+	} else {
+		ans := part2(util.ReadFile("./input.txt"))
+		fmt.Println("Output:", ans)
+	}
+}
+
+func part1(input string) int {
+	bots := parseInput(input)
+
+	strongestBot := bots[0]
+	for _, b := range bots {
+		if b.strength > strongestBot.strength {
+			strongestBot = b
+		}
+	}
+
+	var withinRange int
+	for _, b := range bots {
+		if manhattanDist(b.coords, strongestBot.coords) <= strongestBot.strength {
+			withinRange++
+		}
+	}
+
+	return withinRange
+}
+
+func part2(input string) int {
+	bots := parseInput(input)
+
+	// get the bounds of the cube that all bots are inside of
+	// the answer coordinate will be within this space
+	var minCoord, maxCoord [3]int
+	for i := range minCoord {
+		minCoord[i] = math.MaxInt16
+	}
+	for _, b := range bots {
+		for i := 0; i < 3; i++ {
+			if minCoord[i] > b.coords[i] {
+				minCoord[i] = b.coords[i]
+			}
+			if maxCoord[i] < b.coords[i] {
+				maxCoord[i] = b.coords[i]
+			}
+		}
+	}
+
+	var origin [3]int
+
+	// width of the box
+	boxWidth := maxCoord[0] - minCoord[0]
+
+	// 1. width is used to calculate the eight corners to check.
+	// 2. the reachable bots are counted from each corner
+	// 3. on each iteration, the box is centered around the best corner and the
+	//    width is cut in half until it reaches zero
+	var bestGrid [3]int
+	for boxWidth > 0 {
+		var maxCount int
+
+		for x := minCoord[0]; x < maxCoord[0]+1; x += boxWidth {
+			for y := minCoord[1]; y < maxCoord[1]+1; y += boxWidth {
+				for z := minCoord[2]; z < maxCoord[2]+1; z += boxWidth {
+					current := [3]int{x, y, z}
+					var countInRange int
+					for _, b := range bots {
+						if b.canReach(current) {
+							countInRange++
+						}
+					}
+					if maxCount < countInRange ||
+						(maxCount == countInRange && manhattanDist(bestGrid, origin) > manhattanDist(current, origin)) {
+						maxCount = countInRange
+						bestGrid = current
+					}
+				}
+			}
+		}
+
+		// adjust box size, i.e. min and max coords
+		for i := 0; i < 3; i++ {
+			minCoord[i] = bestGrid[i] - boxWidth
+			maxCoord[i] = bestGrid[i] + boxWidth
+		}
+
+		// shrink searchable box size
+		boxWidth /= 2
+	}
+
+	return manhattanDist(bestGrid, origin)
+}
+
+type nanobot struct {
+	coords   [3]int
+	strength int
+}
+
+func (b nanobot) canReach(coord [3]int) bool {
+	return manhattanDist(coord, b.coords) <= b.strength
+}
+
+func parseInput(input string) []nanobot {
+	var bots []nanobot
+
+	lines := strings.Split(input, "\n")
+	for _, l := range lines {
+		bot := nanobot{}
+		_, err := fmt.Sscanf(l, "pos=<%d,%d,%d>, r=%d", &bot.coords[0], &bot.coords[1], &bot.coords[2], &bot.strength)
+		if err != nil {
+			panic("parsing input line " + err.Error())
+		}
+		bots = append(bots, bot)
+	}
+
+	return bots
+}
+
+func manhattanDist(one, two [3]int) int {
+	var dist int
+	for i := range one {
+		diff := one[i] - two[i]
+		if diff < 0 {
+			diff *= -1
+		}
+		dist += diff
+	}
+	return dist
+}

2018/day23/main_test.go

@@ -0,0 +1,62 @@
+package main
+
+import (
+	"testing"
+
+	"github.com/alexchao26/advent-of-code-go/util"
+)
+
+var example = `pos=<0,0,0>, r=4
+pos=<1,0,0>, r=1
+pos=<4,0,0>, r=3
+pos=<0,2,0>, r=1
+pos=<0,5,0>, r=3
+pos=<0,0,3>, r=1
+pos=<1,1,1>, r=1
+pos=<1,1,2>, r=1
+pos=<1,3,1>, r=1`
+
+var tests1 = []struct {
+	name  string
+	want  int
+	input string
+}{
+	{"example", 7, example},
+	{"actual", 573, util.ReadFile("input.txt")},
+}
+
+func TestPart1(t *testing.T) {
+	for _, tt := range tests1 {
+		t.Run(tt.name, func(t *testing.T) {
+			if got := part1(tt.input); got != tt.want {
+				t.Errorf("part1() = %v, want %v", got, tt.want)
+			}
+		})
+	}
+}
+
+var example2 = `pos=<10,12,12>, r=2
+pos=<12,14,12>, r=2
+pos=<16,12,12>, r=4
+pos=<14,14,14>, r=6
+pos=<50,50,50>, r=200
+pos=<10,10,10>, r=5`
+
+var tests2 = []struct {
+	name  string
+	want  int
+	input string
+}{
+	{"example", 36, example2},
+	{"actual", 107279292, util.ReadFile("input.txt")},
+}
+
+func TestPart2(t *testing.T) {
+	for _, tt := range tests2 {
+		t.Run(tt.name, func(t *testing.T) {
+			if got := part2(tt.input); got != tt.want {
+				t.Errorf("part2() = %v, want %v", got, tt.want)
+			}
+		})
+	}
+}