From f32239d2cb2f85095c44b7c3367291d9c864a1f1 Mon Sep 17 00:00:00 2001
From: alexchao26 <alexchaoo@gmail.com>
Date: Sat, 11 Dec 2021 12:29:05 -0500
Subject: [PATCH] 2021 day11: fun game of life ish thing

---
 2021/day11/main.go      | 122 ++++++++++++++++++++++++++++++++++++++++
 2021/day11/main_test.go |  57 +++++++++++++++++++
 2 files changed, 179 insertions(+)
 create mode 100644 2021/day11/main.go
 create mode 100644 2021/day11/main_test.go

diff --git a/2021/day11/main.go b/2021/day11/main.go
new file mode 100644
index 0000000..bb3bb9e
--- /dev/null
+++ b/2021/day11/main.go
@@ -0,0 +1,122 @@
+package main
+
+import (
+	_ "embed"
+	"flag"
+	"fmt"
+	"math"
+	"strings"
+
+	"github.com/alexchao26/advent-of-code-go/cast"
+	"github.com/alexchao26/advent-of-code-go/util"
+)
+
+//go:embed input.txt
+var input string
+
+func init() {
+	// do this in init (not main) so test file has same input
+	input = strings.TrimRight(input, "\n")
+	if len(input) == 0 {
+		panic("empty input.txt file")
+	}
+}
+
+func main() {
+	var part int
+	flag.IntVar(&part, "part", 1, "part 1 or 2")
+	flag.Parse()
+	fmt.Println("Running part", part)
+
+	ans := flashingOctopiLol(input, part)
+	util.CopyToClipboard(fmt.Sprintf("%v", ans))
+	fmt.Println("Output:", ans)
+}
+
+func flashingOctopiLol(input string, part int) int {
+	grid := parseInput(input)
+
+	var flashed int
+
+	adjacentDiffs := [][2]int{
+		{-1, 0},
+		{-1, -1},
+		{-1, 1},
+		{0, -1},
+		{0, 1},
+		{1, -1},
+		{1, 0},
+		{1, 1},
+	}
+
+	steps := 100
+	if part == 2 {
+		// assume it'll run in less steps than 2^31-1...
+		steps = math.MaxInt32
+	}
+
+	for s := 0; s < steps; s++ {
+		// initial increment and store who will flash
+		var queueToFlash [][2]int
+		for i, row := range grid {
+			for j := range row {
+				grid[i][j]++
+				if grid[i][j] > 9 {
+					queueToFlash = append(queueToFlash, [2]int{i, j})
+				}
+			}
+		}
+
+		// map tracks who has flashed, bc it's a map it'll also help dedupe and its length will be
+		// how many flashed on this step
+		seen := map[[2]int]bool{}
+		for len(queueToFlash) > 0 {
+			front := queueToFlash[0]
+			queueToFlash = queueToFlash[1:]
+			if seen[front] {
+				continue
+			}
+			seen[front] = true
+
+			// increment neighbors
+			for _, d := range adjacentDiffs {
+				r, c := front[0]+d[0], front[1]+d[1]
+				// check in bounds
+				if r < 0 || r >= len(grid) || c < 0 || c >= len(grid[0]) {
+					continue
+				}
+				grid[r][c]++
+				// check if neighbor should flash, seen map will dedupe so don't safeguard here
+				if grid[r][c] > 9 {
+					queueToFlash = append(queueToFlash, [2]int{r, c})
+				}
+			}
+		}
+
+		// part1, track how many have flashed in total
+		flashed += len(seen)
+		// set them all to zero
+		for c := range seen {
+			grid[c[0]][c[1]] = 0
+		}
+
+		// if all octopi flashed, return the step number (1-indexed)
+		if part == 2 && len(seen) == len(grid)*len(grid[0]) {
+			return s + 1
+		}
+	}
+
+	// for part 1
+	return flashed
+}
+
+func parseInput(input string) (ans [][]int) {
+	for _, line := range strings.Split(input, "\n") {
+		var row []int
+		for _, char := range strings.Split(line, "") {
+			row = append(row, cast.ToInt(char))
+		}
+		ans = append(ans, row)
+	}
+	return ans
+}
diff --git a/2021/day11/main_test.go b/2021/day11/main_test.go
new file mode 100644
index 0000000..ce48290
--- /dev/null
+++ b/2021/day11/main_test.go
@@ -0,0 +1,57 @@
+package main
+
+import (
+	"testing"
+)
+
+var example = `5483143223
+2745854711
+5264556173
+6141336146
+6357385478
+4167524645
+2176841721
+6882881134
+4846848554
+5283751526`
+
+func Test_flashingOctopiLol(t *testing.T) {
+	tests := []struct {
+		name  string
+		input string
+		part  int
+		want  int
+	}{
+		{
+			name:  "example",
+			input: example,
+			part:  1,
+			want:  1656,
+		},
+		{
+			name:  "actual",
+			input: input,
+			part:  1,
+			want:  1723,
+		},
+		{
+			name:  "example",
+			input: example,
+			part:  2,
+			want:  195,
+		},
+		{
+			name:  "actual",
+			input: input,
+			part:  2,
+			want:  327,
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if got := flashingOctopiLol(tt.input, tt.part); got != tt.want {
+				t.Errorf("flashingOctopiLol() = %v, want %v", got, tt.want)
+			}
+		})
+	}
+}