2018 day10 - gross 2D grid with moving objects

2018/day10/main.go

@@ -0,0 +1,157 @@
+package main
+
+import (
+	"flag"
+	"fmt"
+	"math"
+	"strings"
+	"time"
+
+	"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 {
+		part1(util.ReadFile("./input.txt"))
+	} else {
+		part2(util.ReadFile("./input.txt"))
+	}
+}
+
+func part1(input string) {
+	postions, velocities := parseInputs(input)
+
+	steps := 0
+
+	prints := 0
+	hasPrinted := false
+	for hasLoneIsland(postions) {
+		move(postions, velocities)
+		steps++
+		fmt.Println("\nsteps run", steps)
+
+		printable := printGrid(postions)
+		if printable != "" {
+			fmt.Println("Steps: ", steps)
+			fmt.Println(printable)
+			time.Sleep(time.Millisecond * 500)
+			hasPrinted = true
+		}
+		// stop printing after things have collided
+		if printable == "" && hasPrinted {
+			return
+		}
+		fmt.Println(prints)
+	}
+}
+
+func part2(input string) {
+	// Note, reused part 1 with a print for the number of steps
+	part1(input)
+}
+
+func parseInputs(input string) (positions [][2]int, velocities [][2]int) {
+	lines := strings.Split(input, "\n")
+	for _, l := range lines {
+		posX := strings.TrimSpace(l[10:16])
+		posY := strings.TrimSpace(l[18:24])
+		velX := strings.TrimSpace(l[36:38])
+		velY := strings.TrimSpace(l[40:42])
+		positions = append(positions, [2]int{util.StrToInt(posX), util.StrToInt(posY)})
+		velocities = append(velocities, [2]int{util.StrToInt(velX), util.StrToInt(velY)})
+	}
+
+	return positions, velocities
+}
+
+// this didn't work unfortunately, letters like K do have "lone islands" along
+// the diagonals
+func hasLoneIsland(grid [][2]int) bool {
+	coords := map[[2]int]bool{}
+	// generate map
+	for _, pos := range grid {
+		coords[pos] = true
+	}
+
+	// iterate through coords again and check if each has a neighbor in the map
+	delta := [][2]int{
+		{-1, 0},
+		{1, 0},
+		{0, -1},
+		{0, 1},
+	}
+	for _, pos := range grid {
+		hasNeighbor := false
+		for _, d := range delta {
+			pos[0] += d[0]
+			pos[1] += d[1]
+
+			if coords[pos] {
+				hasNeighbor = true
+			}
+
+			pos[0] -= d[0]
+			pos[1] -= d[1]
+		}
+		if !hasNeighbor {
+			return true // there is a lone island
+		}
+	}
+	return false
+}
+
+func move(positions [][2]int, velocities [][2]int) {
+	for i := range positions {
+		positions[i][0] += velocities[i][0]
+		positions[i][1] += velocities[i][1]
+	}
+}
+
+func printGrid(positions [][2]int) string {
+	// get bounds
+	left := math.MaxInt16
+	right := -math.MaxInt16
+	top := math.MaxInt16
+	bottom := -math.MaxInt16
+
+	coords := map[[2]int]bool{}
+
+	for _, p := range positions {
+		coords[p] = true
+
+		if p[0] < top {
+			top = p[0]
+		}
+		if p[0] > bottom {
+			bottom = p[0]
+		}
+		if p[1] < left {
+			left = p[1]
+		}
+		if p[1] > right {
+			right = p[1]
+		}
+	}
+
+	if right-left > 20 && bottom-top > 20 {
+		return ""
+	}
+
+	ans := ""
+	for row := top; row <= bottom; row++ {
+		for col := left; col <= right; col++ {
+			if coords[[2]int{row, col}] {
+				ans += "0"
+			} else {
+				ans += " "
+			}
+		}
+		ans += "\n"
+	}
+	return ans
+}