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