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  • Architeuthis@awful.systems
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    11 months ago

    Day 4: Scratchcards

    Late to the party and never done advents before, I liked how this problem reminded me that tree traversal is thing, almost as much as I don’t that so much of my career involves powershell now.

    I’m putting everything up at https://github.com/SpaceAntelope/advent-of-code-2023 except the input files.

    Using command abbreviations like % and ? to keep the horizontal length friendly to lemmy post areas, they are expanded in git.

    Part 2 in Powershell
    function calculate([string]$data) {
      # code for parsing data and calculating matches from pt1 here, check the github link if you like banal regexps
      # returns objects with the relevant fields being the card index and the match count
    }
    
    function calculateAccumulatedCards($data) {
        $cards = calculate $data # do pt1 calculations
    
        $cards 
        | ? MatchCount -gt 0 # otherwise the losing card becomes its own child and the search cycles to overflow
        | % { 
            $children = ($_.Index + 1) .. ($_.Index + $_.MatchCount)  # range of numbers corresponding to indices of cards won
            | % { $cards[$_ - 1] } # map to the actual cards
            | ? { $null -ne $_ }  # filter out overflow when index exceeds input length
    
            $_ | Add-Member -NotePropertyName Children -NotePropertyValue $children # add cards gained as children property
        }
    
        # do depth first search on every card and its branching children while counting every node
        # the recursive function is inlined in the foreach block because it's simpler than referencing it 
        # from outside the parallel scope
        $cards | % -Parallel {
            function traverse($card) {
                $script:count++        
                foreach ($c in $card.Children) { traverse($c) }
            }
            
            $script:count = 0 # script: means it's basically globally scoped
            traverse $_ 
            $script:count # pass node count to pipeline     
        } 
        | measure -sum    
        | % sum
    }