2021 - Day 11

2021/11/go.mod

@@ -0,0 +1,9 @@
+module AoC/2021/11
+
+require AoC/2021/common v0.0.0
+
+require github.com/joho/godotenv v1.4.0 // indirect
+
+replace AoC/2021/common v0.0.0 => ../common
+
+go 1.17

2021/11/go.sum

@@ -0,0 +1,2 @@
+github.com/joho/godotenv v1.4.0 h1:3l4+N6zfMWnkbPEXKng2o2/MR5mSwTrBih4ZEkkz1lg=
+github.com/joho/godotenv v1.4.0/go.mod h1:f4LDr5Voq0i2e/R5DDNOoa2zzDfwtkZa6DnEwAbqwq4=

2021/11/main.go

@@ -0,0 +1,129 @@
+package main
+
+import (
+	aoc "AoC/2021/common"
+	"bufio"
+	"strconv"
+)
+
+func processInput(input *bufio.Scanner) [10][10]int {
+	var octopuses [10][10]int
+
+	for y := 0; input.Scan(); y++ {
+		line := input.Text()
+
+		for x, c := range line {
+			n, _ := strconv.Atoi(string(c))
+
+			octopuses[y][x] = n
+		}
+	}
+
+	return octopuses
+}
+
+func simulate(octopuses [10][10]int) ([10][10]int, int) {
+	// Start with increasing all the energy levels by one
+	counter := 0
+	for y := 0; y < 10; y++ {
+		for x := 0; x < 10; x++ {
+			octopuses[y][x]++
+			if octopuses[y][x] > 9 {
+				counter++
+			}
+		}
+	}
+
+	// Increase the energy levels of neighbours if a flash has to occur
+	// We keep doing this until the number of octopuses ready to flash does not increase
+	flashes := 0 
+	for counter != 0 {
+		for y := 0; y < 10; y++ {
+			for x := 0; x < 10; x++ {
+				if octopuses[y][x] > 9 {
+					octopuses[y][x] = 0
+					flashes++
+					if x != 0 && octopuses[y][x-1] != 0 {
+						octopuses[y][x-1]++
+					}
+					if x != 9 && octopuses[y][x+1] != 0 {
+						octopuses[y][x+1]++
+					}
+					if y != 0 && octopuses[y-1][x] != 0 {
+						octopuses[y-1][x]++
+					}
+					if y != 9 && octopuses[y+1][x] != 0 {
+						octopuses[y+1][x]++
+					}
+					if x != 0 && y != 0 && octopuses[y-1][x-1] != 0 {
+						octopuses[y-1][x-1]++
+					}
+					if x != 9 && y != 0 && octopuses[y-1][x+1] != 0 {
+						octopuses[y-1][x+1]++
+					}
+					if x != 0 && y != 9 && octopuses[y+1][x-1] != 0 {
+						octopuses[y+1][x-1]++
+					}
+					if x != 9 && y != 9 && octopuses[y+1][x+1] != 0 {
+						octopuses[y+1][x+1]++
+					}
+				}
+			}
+		}
+
+		counter = 0
+		for y := 0; y < 10; y++ {
+			for x := 0; x < 10; x++ {
+				if octopuses[y][x] > 9 {
+					counter++
+				}
+			}
+		}
+	}
+
+	return octopuses, flashes
+}
+
+func main() {
+	challenge := aoc.New(2021, 11)
+
+	challenge.Test(`5483143223
+2745854711
+5264556173
+6141336146
+6357385478
+4167524645
+2176841721
+6882881134
+4846848554
+5283751526`, []int{1656, 195})
+
+	challenge.Solution(1, func (input *bufio.Scanner) int {
+		octopuses := processInput(input)
+
+		sum := 0
+		for step := 0; step < 100; step++ {
+			var s int
+			octopuses, s = simulate(octopuses)
+			sum += s
+		}
+
+		return sum
+	})
+
+	challenge.Solution(2, func (input *bufio.Scanner) int {
+		octopuses := processInput(input)
+
+		for step := 0; step < 1000; step++ {
+			var s int
+			octopuses, s = simulate(octopuses)
+			// Return the first step where all octopuses flash at the same time
+			if s == 100 {
+				// +1 is needed as we start counting at 0
+				return step + 1
+			}
+		}
+
+		return -2
+	})
+}