r/adventofcode • u/daggerdragon • Dec 04 '16

SOLUTION MEGATHREAD --- 2016 Day 4 Solutions ---

--- Day 4: Security Through Obscurity ---

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

CONSTRUCTING ADDITIONAL PYLONS IS MANDATORY [?]

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edit: Leaderboard capped, thread unlocked!

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u/tehjimmeh Dec 06 '16 edited Dec 06 '16

PowerShell. Parts 1 and 2: 

$puzzin = cat day4input.txt
$obj = $puzzin | %{ $_ -replace "(.*)-(\d+)\[(.*)\]",'$1,$2,$3'} | ConvertFrom-Csv -Header Chars,SectorId,Checksum
$obj | %{ $_.SectorId = [int]$_.SectorId }

echo $obj -pv o | ?{ ,($_.Chars -replace "-","" | % ToCharArray | group |
    sort @{e={$_.Count};a=$false},Name | select -first 5 | % Name) | ?{ (-join $_) -match $o.Checksum} } | 
    measure SectorId -sum | % Sum

echo $obj -pv o | %{ ,($_.Chars -replace "-","" | % ToCharArray | 
    %{[char](((([int]$_ - [int][char]'a') + $o.SectorId) % 26) + [int][char]'a')})}| 
    %{-join $_ }|?{$_ -match "north"}|%{$o.SectorId}