Added solutions for 14th day: Extended Polymerization

2021/14/second.go

@@ -0,0 +1,98 @@
+package main
+
+// TODO Off by one! I don't know where!!!!!
+// I get  : 3459174981022
+// I need : 3459174981021
+
+import (
+	"bufio"
+	"fmt"
+	"os"
+	"sort"
+	"strings"
+)
+
+type transform struct {
+	first  byte
+	second byte
+	res    byte
+	count  int
+}
+
+type letter struct {
+	value byte
+	count int
+}
+
+var (
+	pairs   []transform
+	letters []letter
+)
+
+func main() {
+	scanner := bufio.NewScanner(os.Stdin)
+
+	scanner.Scan()
+	polymer := scanner.Text()
+out:
+	for i := 0; i < len(polymer); i++ {
+		for j := range letters {
+			if letters[j].value == polymer[i] {
+				letters[j].count++
+				continue out
+			}
+		}
+		letters = append(letters, letter{polymer[i], 1})
+	}
+	scanner.Scan()
+
+	for scanner.Scan() {
+		line := strings.Split(scanner.Text(), " -> ")
+		pairs = append(pairs, transform{line[0][0], line[0][1], line[1][0], 0})
+	}
+	for i := 0; i < len(polymer)-1; i++ {
+		for j, v := range pairs {
+			if v.first == polymer[i] && v.second == polymer[i+1] {
+				pairs[j].count++
+			}
+		}
+	}
+	newPairs := make([]transform, len(pairs))
+	copy(newPairs, pairs)
+	for s := 1; s < 40; s++ {
+		for j := range newPairs {
+			newPairs[j].count = 0
+		}
+		for _, a := range pairs {
+			if a.count > 0 {
+				for j, b := range pairs {
+					if b.first == a.first && b.second == a.res {
+						newPairs[j].count += a.count
+						break
+					}
+				}
+				for j, b := range pairs {
+					if b.first == a.res && b.second == a.second {
+						newPairs[j].count += a.count
+						break
+					}
+				}
+			}
+		}
+		copy(pairs, newPairs)
+	out2:
+		for _, v := range pairs {
+			for j := range letters {
+				if letters[j].value == v.res {
+					letters[j].count += v.count
+					continue out2
+				}
+			}
+			letters = append(letters, letter{v.res, v.count})
+		}
+	}
+	sort.Slice(letters, func(i, j int) bool {
+		return letters[i].count < letters[j].count
+	})
+	fmt.Println(letters[len(letters)-1].count - letters[0].count)
+}