AdventOfCode2021/11/main.go

package main

import (
	"bufio"
	"fmt"
	"os"
	"strconv"
	"time"
)

func mustAtoi(line byte) int {
	i, _ := strconv.Atoi(string(line))
	return i
}

func main() {
	start := time.Now()
	partOne()
	duration := time.Since(start)
	partTwo()
	duration2 := time.Since(start)
	fmt.Printf("p1: %s, p2: %s\n", duration, duration2-duration)
}

func makeScanner(test bool) *bufio.Scanner {
	var f *os.File
	if test {
		f, _ = os.Open("inputs/testinput")
	} else {
		f, _ = os.Open("inputs/input")
	}
	reader := bufio.NewReader(f)
	return bufio.NewScanner(reader)
}

type octopus struct {
	energy  int
	flashed bool
}

type octopi []octopus // index is col + (row*10)

func (o *octopi) incrementEnergyLevels() {
	for i := range *o {
		(*o)[i].energy++
	}
}

func (o *octopi) flash() bool {
	flash := false
	toIncrement := make([]int, 100)
	for i := range *o {
		if (*o)[i].energy > 9 && !(*o)[i].flashed {
			(*o)[i].flashed = true
			flash = true
			if i > 9 {
				toIncrement[i-10]++ // above
			}
			if i < 90 {
				toIncrement[i+10]++ // below
			}
			if i%10 != 9 {
				toIncrement[i+1]++ // right
			}
			if i%10 != 0 {
				toIncrement[i-1]++ // left
			}
			if i%10 != 0 && i > 9 {
				toIncrement[i-11]++ // above-left
			}
			if i%10 != 9 && i > 9 {
				toIncrement[i-9]++ // above-right
			}
			if i%10 != 0 && i < 90 {
				toIncrement[i+9]++ // below-left
			}
			if i%10 != 9 && i < 90 {
				toIncrement[i+11]++ // below-right
			}
		}
	}
	for i := range toIncrement {
		(*o)[i].energy += toIncrement[i]
	}
	return flash
}

func (o *octopi) reset() int {
	count := 0
	for i := range *o {
		if (*o)[i].energy > 9 {
			count++
			(*o)[i].energy = 0
			(*o)[i].flashed = false
		}
	}
	return count
}

func partOne() {
	scanner := makeScanner(false)

	cave := octopi{}
	for scanner.Scan() {
		line := scanner.Text()
		for i := range line {
			cave = append(cave, octopus{energy: mustAtoi(line[i])})
		}
	}
	total := 0
	for step := 0; step < 100; step++ {
		cave.incrementEnergyLevels()
		for {
			if !cave.flash() {
				break
			}
		}
		total += cave.reset()
	}
	fmt.Println(total)
}

func partTwo() {
	scanner := makeScanner(false)

	cave := octopi{}
	for scanner.Scan() {
		line := scanner.Text()
		for i := range line {
			cave = append(cave, octopus{energy: mustAtoi(line[i])})
		}
	}
	step := 0
	for {
		step++
		cave.incrementEnergyLevels()
		for {
			if !cave.flash() {
				break
			}
		}
		if cave.reset() == 100 {
			break
		}
	}
	fmt.Println(step)
}