117 lines
2.2 KiB
Go
117 lines
2.2 KiB
Go
package daythree
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import (
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"advent-of-code/internal/registry"
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"os"
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"strings"
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)
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func init() {
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registry.Register("2021D3", ParseInput, PartOne, PartTwo)
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}
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func ParseInput(filepath string) []string {
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content, _ := os.ReadFile(filepath)
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return strings.Split(strings.TrimSpace(string(content)), "\n")
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}
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func PartOne(data []string) int {
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bitlen := len(data[0])
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ones := make([]int, bitlen)
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for _, line := range data {
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for i := range bitlen {
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if line[i] == '1' {
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ones[i]++
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}
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}
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}
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var gamma int
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total := len(data)
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for idx := range bitlen {
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gamma <<= 1
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if ones[idx] > total-ones[idx] {
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gamma |= 1
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}
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}
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mask := (1 << bitlen) - 1
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epsilon := mask ^ gamma
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return gamma * epsilon
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}
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func PartTwo(data []string) int {
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bitlen := len(data[0])
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oxygenIndices := make([]int, len(data))
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for idx := range oxygenIndices {
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oxygenIndices[idx] = idx
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}
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co2Indices := make([]int, len(data))
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for idx := range co2Indices {
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co2Indices[idx] = idx
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}
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for indice := 0; indice < bitlen && len(oxygenIndices) > 1; indice++ {
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ones := 0
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for _, idx := range oxygenIndices {
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if data[idx][indice] == '1' {
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ones++
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}
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}
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target := byte('1')
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if ones*2 < len(oxygenIndices) {
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target = '0'
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}
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writeIdx := 0
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for readIdx := 0; readIdx < len(oxygenIndices); readIdx++ {
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if data[oxygenIndices[readIdx]][indice] == target {
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oxygenIndices[writeIdx] = oxygenIndices[readIdx]
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writeIdx++
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}
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}
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oxygenIndices = oxygenIndices[:writeIdx]
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}
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for idx := 0; idx < bitlen && len(co2Indices) > 1; idx++ {
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ones := 0
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for _, indice := range co2Indices {
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if data[indice][idx] == '1' {
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ones++
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}
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}
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target := byte('0')
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if ones*2 < len(co2Indices) {
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target = '1'
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}
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writeIdx := 0
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for readIdx := 0; readIdx < len(co2Indices); readIdx++ {
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if data[co2Indices[readIdx]][idx] == target {
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co2Indices[writeIdx] = co2Indices[readIdx]
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writeIdx++
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}
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}
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co2Indices = co2Indices[:writeIdx]
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}
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oxygenRating := 0
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for _, char := range data[oxygenIndices[0]] {
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oxygenRating <<= 1
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if char == '1' {
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oxygenRating |= 1
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}
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}
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co2Rating := 0
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for _, char := range data[co2Indices[0]] {
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co2Rating <<= 1
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if char == '1' {
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co2Rating |= 1
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}
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}
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return oxygenRating * co2Rating
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}
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