Day 14 solution

fourteen/polymer.go

@@ -0,0 +1,146 @@
+package fourteen
+
+import (
+	"bufio"
+	"fmt"
+	"os"
+)
+
+type polymer struct {
+	template string
+	rules    map[string]string
+}
+
+func (p *polymer) load(filename string) error {
+	file, err := os.Open(filename)
+	if err != nil {
+		return err
+	}
+	defer file.Close()
+	scanner := bufio.NewScanner(file)
+
+	p.rules = map[string]string{}
+	scannedTemplate := false
+	for scanner.Scan() {
+		if !scannedTemplate {
+			p.template = scanner.Text()
+
+			scannedTemplate = true
+			continue
+		}
+
+		if scanner.Text() == "" {
+			continue
+		}
+
+		var pair, insert string
+		if count, err := fmt.Sscanf(scanner.Text(), "%s -> %s", &pair, &insert); count != 2 || err != nil {
+			return fmt.Errorf("expected to scan 2 values from %q, found %d: %w", scanner.Text(), count, err)
+		}
+		p.rules[pair] = insert
+	}
+
+	return nil
+}
+
+func (p *polymer) elementCount(size int) int {
+	result := p.step(size)
+	elemCounts := map[rune]int{}
+
+	for _, r := range result {
+		elemCounts[r]++
+	}
+
+	min := len(result)
+	max := 0
+	for _, v := range elemCounts {
+		if v < min {
+			min = v
+		}
+
+		if v > max {
+			max = v
+		}
+	}
+
+	return max - min
+}
+
+func (p *polymer) elementCountMap(size int) int {
+	_, counts := p.stepMap(size)
+
+	min := -1
+	max := -1
+	for _, v := range counts {
+		if v < min || min == -1 {
+			min = v
+		}
+
+		if v > max {
+			max = v
+		}
+	}
+
+	return max - min
+}
+
+func (p *polymer) stepMap(steps int) (map[string]int, map[string]int) {
+	pairs := map[string]int{}
+	counts := map[string]int{}
+
+	// Build initial pairs and counts from template
+	for i := 0; i < len(p.template)-1; i++ {
+		// Count first element from pair
+		counts[string(p.template[i])]++
+		pairs[fmt.Sprintf("%c%c", p.template[i], p.template[i+1])]++
+		// If this is the last pair add the second element
+		if i == len(p.template)-2 {
+			counts[string(p.template[i+1])]++
+		}
+	}
+
+	for i := 0; i < steps; i++ {
+		pairs, counts = p.stepMapOne(pairs, counts)
+	}
+
+	return pairs, counts
+}
+
+func (p *polymer) stepMapOne(pairs map[string]int, counts map[string]int) (map[string]int, map[string]int) {
+	newPairs := map[string]int{}
+	for k, v := range pairs {
+		result := p.rules[k]
+		counts[result] += (1 * v)
+		pair1 := fmt.Sprintf("%c%s", k[0], result)
+		pair2 := fmt.Sprintf("%s%c", result, k[1])
+		newPairs[pair1] += 1 * v
+		newPairs[pair2] += 1 * v
+	}
+
+	return newPairs, counts
+}
+
+func (p *polymer) step(steps int) string {
+	seed := p.template
+	for i := 0; i < steps; i++ {
+		seed = p.stepOne(seed)
+	}
+
+	return seed
+}
+
+func (p *polymer) stepOne(from string) string {
+	result := ""
+	for i := 0; i < len(from)-1; i++ {
+		// Add first element from pair
+		result += string(from[i])
+		// Lookup and add element result from pair
+		pair := fmt.Sprintf("%c%c", from[i], from[i+1])
+		result += p.rules[pair]
+		// If this is the last pair add the second element
+		if i == len(from)-2 {
+			result += string(from[i+1])
+		}
+	}
+	return result
+}