2021-advent-10.scala

import java.nio.file.{Files,Paths}
import scala.collection.mutable.ArrayDeque
import scala.collection.mutable


val mapping = Map(
    ']' -> '[',
    ')' -> '(',
    '}' -> '{',
    '>' -> '<'
)

val reverseMapping = mapping.map((k,v) => (v,k)).toMap


val scoring = Map(
    ')' -> 3,
    ']' -> 57,
    '}' -> 1197,
    '>' -> 25137,
)

def readLines(input: String) = Files.readString(Paths.get(input)).split("\n")

def countErrorScore(line:String) : (ArrayDeque[Char], Int)  = 
    val deque = ArrayDeque.empty[Char]
    for c <- line do
        c match 
            case '[' | '(' | '{' | '<' => deque.prepend(c)
            case ']' | ')' | '}' | '>' => 
                if deque.isEmpty then
                    return (deque, scoring(c))
                if mapping(c) !=  deque.removeHead() then
                    return (deque, scoring(c))
        
    
    (deque,0)


def buildCompletion(chars: ArrayDeque[Char]): String =
    val sb = mutable.StringBuilder(chars.length)
    while(chars.nonEmpty)
        sb += reverseMapping(chars.removeHead())
    sb.result()

    

def task1(input: String) = 
    val lines = readLines(input)
    val scores = for line <- lines 
        yield countErrorScore(line)._2
    val sum = scores.sum
    println(s"Day10 Task1 $input: ${sum}")
    

def scoreCompletion(completion: String): Int =
    val scores = completion.map ( _ match
        case ')' => 1
        case ']' => 2
        case '}' => 3
        case '>' => 4
    )
    scores.foldLeft(0)((acc, el) => acc * 5 + el)

def task2(input: String) = 
    val toComplete = for 
        line <- readLines(input)
        (deque, score) = countErrorScore(line) if score == 0
    yield deque

    val scores = for it <- toComplete yield
        scoreCompletion(buildCompletion(it))

    val finalScore = scores.sorted.apply(scores.length / 2)
    println(s"Day10 Task2 $input: ${finalScore}")



@main def Day10() = 
    task1("example.txt")
    task2("example.txt")