Day 11

Author: mjlshen

day11/input.txt

@@ -0,0 +1,10 @@
+6111821767
+1763611615
+3512683131
+8582771473
+8214813874
+2325823217
+2222482823
+5471356782
+3738671287
+8675226574

day11/main.go

@@ -0,0 +1,128 @@
+package main
+
+import (
+"bufio"
+"fmt"
+"os"
+"strconv"
+)
+
+func main() {
+fmt.Printf("Part 1: %d\n", numFlashes("input.txt", 100))
+fmt.Printf("Part 2: %d\n", allFlash("input.txt"))
+}
+
+type Coord struct {
+i, j int
+}
+
+type Octopi struct {
+grid [][]int
+flashes int
+}
+
+// allFlash returns the step at which all octopi flash
+func allFlash(path string) int {
+octopi := parseOctopi(path)
+prev := octopi.flashes
+
+for i := 0; ; i++ {
+octopi.step()
+if octopi.flashes-prev == 100 {
+return i + 1
+} else {
+prev = octopi.flashes
+}
+}
+}
+
+// numFlashes returns the number of flashes for a given octopi grid after some steps
+func numFlashes(path string, steps int) int {
+octopi := parseOctopi(path)
+
+for i := 0; i < steps; i++ {
+octopi.step()
+}
+
+return octopi.flashes
+}
+
+func (o *Octopi) step() {
+// Increment each octopus in the grid by 1
+for i := range o.grid {
+for j := range o.grid[i] {
+o.grid[i][j]++
+}
+}
+
+// For each octopus, if it's level is > 9, increment its neighbors
+// up/down/diagonally by 1, and continue until the grid is stable
+prev := 0
+flashed := map[Coord]bool{}
+for {
+for i := range o.grid {
+for j := range o.grid[i] {
+sweep := []Coord{
+{i - 1, j - 1},
+{i - 1, j},
+{i - 1, j + 1},
+{i, j - 1},
+{i, j + 1},
+{i + 1, j - 1},
+{i + 1, j},
+{i + 1, j + 1},
+}
+if o.grid[i][j] > 9 {
+if _, ok := flashed[Coord{i, j}]; !ok {
+for _, coord := range sweep {
+if coord.i >= 0 && coord.i < len(o.grid) && coord.j >= 0 && coord.j < len(o.grid[i]) {
+o.grid[coord.i][coord.j]++
+}
+}
+flashed[Coord{i, j}] = true
+}
+}
+}
+}
+if prev == len(flashed) {
+break
+} else {
+prev = len(flashed)
+}
+}
+
+// For each octopus, if its level is > 9, it flashes and its level becomes 0
+for i := range o.grid {
+for j := range o.grid[i] {
+if o.grid[i][j] > 9 {
+o.grid[i][j] = 0
+o.flashes++
+}
+}
+}
+}
+
+func parseOctopi(path string) *Octopi {
+var octopi [][]int
+
+file, err := os.Open(path)
+if err != nil {
+panic(err)
+}
+defer file.Close()
+
+scanner := bufio.NewScanner(file)
+for scanner.Scan() {
+var line []int
+for _, c := range scanner.Text() {
+level, err := strconv.Atoi(string(c))
+if err != nil {
+panic(err)
+}
+line = append(line, level)
+}
+octopi = append(octopi, line)
+}
+
+return &Octopi{grid: octopi, flashes: 0}
+}

day11/main_test.go

@@ -0,0 +1,48 @@
+package main
+
+import "testing"
+
+func TestNumFlashes(t *testing.T) {
+tests := []struct {
+input string
+steps int
+expected int
+}{
+{
+input: "test.txt",
+steps: 10,
+expected: 204,
+},
+{
+input: "test.txt",
+steps: 100,
+expected: 1656,
+},
+}
+
+for _, test := range tests {
+actual := numFlashes(test.input, test.steps)
+if actual != test.expected {
+t.Errorf("Expected %d, but got %d", test.expected, actual)
+}
+}
+}
+
+func TestAllFlash(t *testing.T) {
+tests := []struct {
+input string
+expected int
+}{
+{
+input: "test.txt",
+expected: 195,
+},
+}
+
+for _, test := range tests {
+actual := allFlash(test.input)
+if actual != test.expected {
+t.Errorf("Expected %d, but got %d", test.expected, actual)
+}
+}
+}

day11/test.txt

@@ -0,0 +1,10 @@
+5483143223
+2745854711
+5264556173
+6141336146
+6357385478
+4167524645
+2176841721
+6882881134
+4846848554
+5283751526