add day 6

day-6/main.go

@@ -0,0 +1,120 @@
+/* Day 6: Lanternfish */
+package main
+
+import (
+	"AoC2021/utils/log"
+	"AoC2021/utils/timer"
+	"bufio"
+	"fmt"
+	"os"
+	"strconv"
+	"strings"
+)
+
+const REPRODUCE_DAYS = 7
+const JUVINILE_DAYS = 2
+
+func check(e error) {
+	if e != nil {
+		log.Println(log.DEBUG, "Oh snap!")
+		panic(e)
+	}
+}
+
+func main() {
+	log.LOG_LEVEL = log.NORMAL
+
+	log.Println(log.NORMAL, "--- Day 6: Lanternfish ---")
+	timer.Start()
+	part1()
+	timer.Tick()
+	log.Println(log.NORMAL)
+
+	part2()
+	timer.Tick()
+	log.Println(log.NORMAL)
+}
+
+func part1() {
+	log.Println(log.NORMAL, "* Part 1 *")
+	log.Println(log.NORMAL, " Goal: Find a way to simulate lanternfish.")
+	log.Println(log.NORMAL, " Answer: How many lanternfish would there be after 80 days?")
+
+	justDoIt(80)
+}
+
+func part2() {
+	log.Println(log.NORMAL, "* Part 2 *")
+	log.Println(log.NORMAL, " Goal: Would they take over the entire ocean?")
+	log.Println(log.NORMAL, " Answer: How many lanternfish would there be after 256 days?")
+
+	justDoIt(256)
+}
+
+func justDoIt(total_days int) {
+	input, err := os.Open("./input.txt")
+	check(err)
+	defer input.Close()
+
+	scanner := bufio.NewScanner(input)
+
+	// Keeping track of each individual fish is stupid
+	// Instead track how *many* fish are at each gestation period
+	groupCount := make([]uint, REPRODUCE_DAYS+JUVINILE_DAYS)
+
+	startingCount := 0
+	lines := 0
+
+	// Read in all the starting fish
+	for scanner.Scan() {
+		startingFish := strings.Split(scanner.Text(), ",")
+		startingCount += len(startingFish)
+
+		lines++
+		// A fish read in as day '3' will be counted at index '2' since day '0' is a valid day
+		for _, fish := range startingFish {
+			day, err := strconv.Atoi(fish)
+			check(err)
+			if day > REPRODUCE_DAYS {
+				panic(fmt.Sprintf("Read an invalid value for fish day: %d", day))
+			}
+			groupCount[day] += 1
+		}
+	}
+	log.Printf(log.NORMAL, "Parsed %d fish from %d lines from input\n", startingCount, lines)
+	log.Println(log.DEBUG, "Fishes group count", groupCount)
+	log.Println(log.DEBUG)
+
+	// Begin the simulation
+	for day := 0; day < total_days; day++ {
+		// keep track of this for later
+		readyToReproduce := groupCount[0]
+		log.Printf(log.DEBUG, "Day %d starts with %d fish ", day+1, sumFish(groupCount))
+		log.Print(log.DEBUG, groupCount)
+		// shift down ALL groups
+		for fishDay := 1; fishDay < REPRODUCE_DAYS+JUVINILE_DAYS; fishDay++ {
+			groupCount[fishDay-1] = groupCount[fishDay]
+		}
+		// Spawn new fish
+		groupCount[REPRODUCE_DAYS+JUVINILE_DAYS-1] = readyToReproduce
+		// Add the fish that reproduced back into the pool
+		groupCount[REPRODUCE_DAYS-1] += readyToReproduce
+		log.Printf(log.DEBUG, " and ends with %d fish ", sumFish((groupCount)))
+		log.Print(log.DEBUG, groupCount)
+		log.Println(log.DEBUG)
+	}
+
+	// Add them all up and be sad that there is no map reduce in golang
+	totalCount := sumFish(groupCount)
+
+	log.Printf(log.NORMAL, "At the end of %d days there were %d fish\n", total_days, totalCount)
+}
+
+func sumFish(counts []uint) uint {
+	total := uint(0)
+	for _, count := range counts {
+		total += count
+	}
+
+	return total
+}