2021 - Day 6

2021/6/go.mod

@@ -0,0 +1,9 @@
+module AoC/2021/6
+
+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

2021/6/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=

2021/6/main.go

@@ -0,0 +1,92 @@
+package main
+
+import (
+	aoc "AoC/2021/common"
+	"bufio"
+	"strconv"
+	"strings"
+)
+
+func main() {
+	aoc := aoc.New(2021, 6)
+
+	aoc.Test(`3,4,3,1,2`, []int{5934, 26984457539})
+
+	// This is a very naive solution, it works for part 1 but not for part 2
+	aoc.Solution(1, func (input *bufio.Scanner) int {
+		var fish []int
+
+		input.Scan()
+		line := input.Text()
+		numbers := strings.Split(line, ",")
+
+		for _, str := range numbers {
+			n, err := strconv.Atoi(str)
+			if err != nil {
+				panic(err)
+			}
+
+			fish = append(fish, n)
+		}
+
+		days := 80
+		for day := 1; day <= days; day++ {
+			add := 0
+
+			for i := range fish {
+				if fish[i] == 0 {
+					add++
+					fish[i] = 6
+				} else {
+					fish[i]--
+				}
+			}
+
+			for i := 0; i < add; i++ {
+				fish = append(fish, 8)
+			}
+		}
+
+		return len(fish)
+	})
+
+	// This is a much more elegant solution, it can also be used to solve part 1
+	aoc.Solution(2, func (input *bufio.Scanner) int {
+		fish := make(map[int]int)
+		input.Scan()
+		line := input.Text()
+		numbers := strings.Split(line, ",")
+
+		for _, str := range numbers {
+			n, err := strconv.Atoi(str)
+			if err != nil {
+				panic(err)
+			}
+
+			fish[n]++
+		}
+
+		days := 256
+		for day := 1; day <= days; day++ {
+			temp := make(map[int]int)
+
+			for n, c := range fish {
+				if n == 0 {
+					temp[8] += c
+					temp[6] += c
+				} else {
+					temp[n-1] += c
+				}
+			}
+
+			fish = temp
+		}
+
+		sum := 0
+		for _, c := range fish {
+			sum += c
+		}
+
+		return sum
+	})
+}