127 lines
2.7 KiB
Go
127 lines
2.7 KiB
Go
package day_08
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import (
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"fmt"
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"regexp"
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"strings"
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"rpjosh.de/adventOfCode/pkg/utils"
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)
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type Day struct{}
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func (d *Day) Part1(in string) string {
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inSplit := strings.Split(in, "\n")
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// Initialize variables
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instructions := inSplit[0]
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line := 0
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instructionCounter := 0
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instructionRegex := regexp.MustCompile(`[ \(](?P<primary>\w+)[,\)]`)
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steps := 0
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// Build indexed map for better performance
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instructionMap := make(map[string]int, 0)
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for i, val := range inSplit {
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if i > 1 && len(val) > 2 {
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v := val[0:3]
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instructionMap[v] = i
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// Found start
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if v == "AAA" {
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line = i
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}
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}
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}
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// Find destination
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for {
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// Start by first instruction on end
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if instructionCounter >= len(instructions) {
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instructionCounter = 0
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}
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// Get left or right
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instructionIndex := 0
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if instructions[instructionCounter] == 'R' {
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instructionIndex = 1
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}
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// Get the next instruction to move on
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next := instructionRegex.FindAllStringSubmatch(inSplit[line], -1)[instructionIndex]
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line = instructionMap[next[1]]
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//logger.Debug("Going to %q on line %d", next[1], line)
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steps++
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instructionCounter++
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// Did we reach the end?
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if strings.HasPrefix(next[1], "ZZZ") {
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break
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}
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}
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return fmt.Sprintf("%d", steps)
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}
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func (d *Day) Part2(in string) string {
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inSplit := strings.Split(in, "\n")
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// Initialize variables
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instructions := inSplit[0]
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starts := make([]int, 0)
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stepsByStarts := make([]int, 0)
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instructionRegex := regexp.MustCompile(`[ \(](?P<primary>\w+)[,\)]`)
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// Build map for better performance
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instructionMap := make(map[string]int, 0)
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for i, val := range inSplit {
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if i > 1 && len(val) > 2 {
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v := val[0:3]
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instructionMap[v] = i
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// Found start
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if v[2] == 'A' {
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starts = append(starts, i)
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}
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}
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}
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// Find for each starting point the amount of steps that we need to go to the
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// first 'Z'.
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// The input data makes sure that the way back from a Z Node to another Z Node
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// is always the same as from start to the first Z node.
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// How would you find out without looping the first time!
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for _, val := range starts {
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steps := 0
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line := val
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instructionCounter := 0
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for {
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// Start by first instruction on end
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if instructionCounter >= len(instructions) {
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instructionCounter = 0
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}
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// Get left or right
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instructionIndex := 0
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if instructions[instructionCounter] == 'R' {
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instructionIndex = 1
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}
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next := instructionRegex.FindAllStringSubmatch(inSplit[line], -1)[instructionIndex]
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line = instructionMap[next[1]]
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//logger.Debug("%d. Going to %q on line %d", i, next[1], line)
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steps++
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instructionCounter++
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if next[1][2] == 'Z' {
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break
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}
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}
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stepsByStarts = append(stepsByStarts, steps)
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}
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return fmt.Sprintf("%d", utils.CalculateLCM(stepsByStarts...))
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}
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