// --- Day 8: Haunted Wasteland ---
// You're still riding a camel across Desert Island when you spot a sandstorm
// quickly approaching. When you turn to warn the Elf, she disappears before
// your eyes! To be fair, she had just finished warning you about ghosts a few
// minutes ago.
//
// One of the camel's pouches is labeled "maps" - sure enough, it's full of
// documents (your puzzle input) about how to navigate the desert. At least,
// you're pretty sure that's what they are; one of the documents contains a
// list of left/right instructions, and the rest of the documents seem to
// describe some kind of network of labeled nodes.
//
// It seems like you're meant to use the left/right instructions to navigate
// the network. Perhaps if you have the camel follow the same instructions, you
// can escape the haunted wasteland!
//
// After examining the maps for a bit, two nodes stick out: AAA and ZZZ. You
// feel like AAA is where you are now, and you have to follow the left/right
// instructions until you reach ZZZ.
//
// This format defines each node of the network individually. For example:
//
// RL
//
// AAA = (BBB, CCC)
// BBB = (DDD, EEE)
// CCC = (ZZZ, GGG)
// DDD = (DDD, DDD)
// EEE = (EEE, EEE)
// GGG = (GGG, GGG)
// ZZZ = (ZZZ, ZZZ)
//
// Starting with AAA, you need to look up the next element based on the next
// left/right instruction in your input. In this example, start with AAA and go
// right (R) by choosing the right element of AAA, CCC. Then, L means to choose
// the left element of CCC, ZZZ. By following the left/right instructions, you
// reach ZZZ in 2 steps.
//
// Of course, you might not find ZZZ right away. If you run out of left/right
// instructions, repeat the whole sequence of instructions as necessary: RL
// really means RLRLRLRLRLRLRLRL... and so on. For example, here is a situation
// that takes 6 steps to reach ZZZ:
//
// LLR
//
// AAA = (BBB, BBB)
// BBB = (AAA, ZZZ)
// ZZZ = (ZZZ, ZZZ)
//
// Starting at AAA, follow the left/right instructions. How many steps are
// required to reach ZZZ?

import java.io.*

fun <T> Sequence<T>.repeat() = sequence { while (true) yieldAll(this@repeat) }

class Fork(val left: String, val right: String) {
  fun next(turn: Char): String {
    if (turn == 'L') return this.left
    return this.right
  }
}

val lines = File("input.txt").readLines()
val directions = lines[0]
val map = lines.drop(2).associate {
  it.substring(0..2) to Fork(it.substring(7..9), it.substring(12..14))
}
var position = "AAA"
val result = directions.asSequence().repeat().takeWhile {
  position = map[position]!!.next(it)
  position != "ZZZ"
}.count() + 1
println(result)
