2021 - Day 14

2021/14/go.mod

@@ -0,0 +1,9 @@
+module AoC/2021/14
+
+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

2021/14/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=

2021/14/main.go

@@ -0,0 +1,180 @@
+package main
+
+import (
+	aoc "AoC/2021/common"
+	"bufio"
+	"fmt"
+	"sort"
+	"strings"
+)
+
+func main() {
+	challenge := aoc.New(2021, 14)
+
+	challenge.Test(`NNCB
+
+CH -> B
+HH -> N
+CB -> H
+NH -> C
+HB -> C
+HC -> B
+HN -> C
+NN -> C
+BH -> H
+NC -> B
+NB -> B
+BN -> B
+BB -> N
+BC -> B
+CC -> N
+CN -> C`, []int{1588, 2188189693529})
+
+	challenge.Solution(1, func (input *bufio.Scanner) int {
+		subs := make(map[string]string, 0)
+
+		input.Scan()
+		polymer := input.Text()
+		fmt.Printf("Template:\t%s\n", polymer)
+
+		input.Scan()
+		for input.Scan() {
+			line := input.Text()
+			s := strings.Split(line, " ")
+
+			subs[s[0]] = s[2]
+		}
+
+		for step := 1; step <= 10; step++ {
+			// First find all the matches
+			indices := make(map[int]string, 0)
+			for k, v := range subs {
+				index := 0
+				for true {
+					i := strings.Index(polymer[index:], k)
+					if i == -1 {
+						break
+					}
+
+					index += i + 1
+					indices[index] = v
+				}
+			}
+
+			keys := make([]int, len(indices))
+			i := 0
+			for k := range indices {
+				keys[i] = k
+				i++
+			}
+			sort.Ints(keys)
+
+			// Insert the new chars
+			inserted := 0
+			for _, k := range keys {
+				index := k + inserted
+				inserted++
+
+				polymer = polymer[:index] + indices[k] + polymer[index:]
+			}
+
+			// fmt.Printf("Step %d:\t\t%s\n", step, polymer)
+		}
+
+		min := -1
+		max := -1
+		for _, v := range subs {
+			c := strings.Count(polymer, v)
+
+			if c < min || min == -1 {
+				min = c
+			}
+
+			if c > max || max == -1 {
+				max = c
+			}
+		}
+
+		return max - min
+	})
+
+	challenge.Solution(2, func (input *bufio.Scanner) int {
+		subs := make(map[string]string, 0)
+
+		input.Scan()
+		polymer := input.Text()
+		fmt.Printf("Template:\t%s\n", polymer)
+
+		// Create the mapping
+		input.Scan()
+		for input.Scan() {
+			line := input.Text()
+			s := strings.Split(line, " ")
+
+			subs[s[0]] = s[2]
+		}
+
+		// Find all different pairs in the initial polymer
+		pairs := make(map[string]int, 0)
+		for k := range subs {
+			pairs[k] = 0
+
+			index := 0
+			for true {
+				i := strings.Index(polymer[index:], k)
+				if i == -1 {
+					break
+				}
+
+				index += i + 1
+				pairs[k]++
+			}
+		}
+
+		counter := make(map[string]int, 0)
+		for i := range polymer {
+			counter[string(polymer[i])]++
+		}
+
+		// Execute each step
+		for step := 1; step <= 40; step++ {
+			pairsNew := make(map[string]int, 0)
+			for p, c := range pairs {
+				// Each pair will form a new 3 long segment
+				n := string(p[0]) + subs[p] + string(p[1])
+				counter[subs[p]] += c
+
+				// Find the two pairs in this segment
+				// These are added to the new list of pairs
+				for k := range subs {
+					index := 0
+					for true {
+						i := strings.Index(n[index:], k)
+						if i == -1 {
+							break
+						}
+
+						index += i + 1
+						pairsNew[k] += c
+					}
+				}
+			}
+
+			pairs = pairsNew
+		}
+
+		min := -1
+		max := -1
+		for _, c := range counter {
+			if c < min || min == -1 {
+				min = c
+			}
+
+			if c > max || max == -1 {
+				max = c
+			}
+		}
+
+		return max - min
+	})
+}