68 lines
1.6 KiB
Go
68 lines
1.6 KiB
Go
package d14
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import (
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"strings"
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"golang.org/x/exp/maps"
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"golang.org/x/exp/slices"
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)
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func reduce[S any, A any](slice []S, f func(elm S, acc A) A, acc A) A {
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for _, elm := range slice {
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acc = f(elm, acc)
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}
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return acc
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}
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func makePairs(template string) map[string]int {
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pairs := make(map[string]int)
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for i := 0; i < len(template)-1; i++ {
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pairs[string(template[i])+string(template[i+1])] = 1
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}
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return pairs
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}
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func templateAndInstructions(in string) (string, map[string]string) {
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parts := strings.Split(strings.TrimSpace(in), "\n\n")
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instructions := make(map[string]string)
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for _, pair := range strings.Split(parts[1], "\n") {
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mapping := strings.Split(pair, " -> ")
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instructions[mapping[0]] = mapping[1]
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}
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return parts[0], instructions
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}
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func count(template string, instructions map[string]string, runs int) map[string]int {
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init := func(char string, acc map[string]int) map[string]int { acc[char]++; return acc }
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counts := reduce(strings.Split(template, ""), init, make(map[string]int))
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pairs := makePairs(template)
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for i := 0; i < runs; i++ {
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for pair, count := range maps.Clone(pairs) {
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left := pair[:1]
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right := pair[1:]
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middle := instructions[pair]
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pairs[pair] -= count
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pairs[left+middle] += count
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pairs[middle+right] += count
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counts[middle] += count
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}
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}
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return counts
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}
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func countPolymer(in string, runs int) int {
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template, instructions := templateAndInstructions(in)
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counts := maps.Values(count(template, instructions, runs))
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slices.Sort(counts)
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max := counts[len(counts)-1]
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min := counts[0]
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return max - min
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}
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func P1(in string) int {
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return countPolymer(in, 10)
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}
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