Day05HowAboutANiceGameOfChess.kt

package adventofcode.year2016

import adventofcode.Puzzle
import adventofcode.PuzzleInput
import adventofcode.common.String.md5

class Day05HowAboutANiceGameOfChess(customInput: PuzzleInput? = null) : Puzzle(customInput) {
    override val name = "How About a Nice Game of Chess?"

    override fun partOne() =
        generateSequence(0 to "") { (index, password) ->
            val hash = "$input$index".md5()

            when (hash.substring(0, 5)) {
                "00000" -> index + 1 to "$password${hash[5]}"
                else -> index + 1 to password
            }
        }
            .first { (_, password) -> password.length == PASSWORD_LENGTH }
            .second

    override fun partTwo() =
        generateSequence(0 to emptyMap<Int, Char>()) { (index, password) ->
            val hash = "$input$index".md5()
            val prefix = hash.substring(0, 5)
            val position = hash[5].digitToIntOrNull()
            val character = hash[6]

            when {
                prefix != "00000" -> index + 1 to password
                position !in 0 until PASSWORD_LENGTH -> index + 1 to password
                password.containsKey(position) -> index + 1 to password
                else -> index + 1 to password + mapOf(position!! to character)
            }
        }
            .first { (_, password) -> password.size == PASSWORD_LENGTH }
            .second
            .toSortedMap()
            .values
            .joinToString("")

    companion object {
        private const val PASSWORD_LENGTH = 8
    }
}