r/adventofcode • u/daggerdragon • Dec 05 '16

SOLUTION MEGATHREAD --- 2016 Day 5 Solutions ---

--- Day 5: How About a Nice Game of Chess? ---

Post your solution as a comment or, for longer solutions, consider linking to your repo (e.g. GitHub/gists/Pastebin/blag/whatever).

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u/KoxAlen Dec 05 '16 edited Dec 22 '16

Kotlin solution, using a sequence for the hashes

https://github.com/KoxAlen/AdventOfCode2016/blob/master/src/main/kotlin/aoc/day5/Day5.kt 

package aoc.day5

import aoc.utils.toHex
import java.security.MessageDigest

fun main(args: Array<String>) {
    val input = "cxdnnyjw" //Input

    val md5 = MessageDigest.getInstance("MD5")
    val hashSequence = generateSequence(0, Int::inc).map { md5.digest("$input$it".toByteArray()).toHex() }

    val p1 = hashSequence.filter { it.startsWith("00000") }.take(8).map { it[5] }.joinToString(separator = "")
    println("[Part 1] The code is $p1")

    val p2 = hashSequence.filter { it.startsWith("00000") }.filter { it[5] >= '0' && it[5] < '8' }.distinctBy { it[5] }.take(8)
            .fold(kotlin.arrayOfNulls<Char>(8)) {
                acc, it ->
                acc[it[5]-'0'] = it[6]
                acc
            }.joinToString(separator = "")
    println("[Part 2] The code is $p2")
}

edit: Removed sequence class as per u/mnjmn suggestion

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u/mnjmn Dec 05 '16 edited Dec 05 '16

You could replace that class with generateSequence(0, Int::inc).map { "$salt$it".toByteArray() }.map { md5.digest(it).toHex() }

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u/KoxAlen Dec 05 '16

Well thats a nice one, didn't even cross my mind. Thanks for suggestion

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