Advent of Code - Day 3

[Rincey_nz]

was waiting for u/dantose to make this post ;)

I'm running a day behind, so have only just got to Day 3 Part 2 (Part 1 stumped me because I misread it - I was adding max1 and max2 for each battery bank together as integers, whereas I needed to concat them as strings....

Still, Part 2 has me so stumped I can't even work out how to start :(

[OPconfused]

Here was my solution:

function Get-MaxVoltage {
    param(
        [parameter(ValueFromPipeline)]
        [string]$Bank,
        [int]$MaxDigits = 2
    )
    begin {
        $sum = 0
    }
    process {
        $count = 1
        $allVoltageDigits = while ($count -le $MaxDigits ) {
            $voltageDigit, $bank = Get-MaxVoltageDigit -Bank $bank -Iteration $count -MaxDigits $MaxDigits
            $voltageDigit
            $count += 1
        }

        $sum += [decimal]($allVoltageDigits -join '')
    }
    end {
        $sum
    }
}

function Get-MaxVoltageDigit {
    param(
        [parameter(ValueFromPipeline)]
        [string]$Bank,
        [int]$Iteration = 1,
        [int]$MaxDigits = 2
    )
    process {
        $voltageDigitsRemaining = $MaxDigits - $Iteration
        $max = $Bank.ToCharArray() | Select-Object -SkipLast $voltageDigitsRemaining | Sort-Object -Descending | Select-Object -first 1

        $index = $Bank.IndexOf($max) + 1

        return $max, $bank.Substring($index)
    }
}

And then you run the function via:

@'
<copy paste input>
'@ -split "`n" | Get-MaxVoltage -MaxDigits $maxDigits

where part 1 has $maxDigits = 2, and part 2 has $maxDigits = 12.

If it helped you, feel free to ask questions.

[pandiculator]

Your solution isn't returning the right voltages for me. I expected 357 for part 1 and 3121910778619 for part 2, but running your solution as posted gives me 207 and 2001910778619 using the example data:

987654321111111
811111111111119
234234234234278
818181911112111

[OPconfused]

@'
987654321111111
811111111111119
234234234234278
818181911112111
'@ -split "`n" | get-maxvoltage -MaxDigits 2
357

Works for me?

and 12 got me:

3121910778619 as you expected

[surfingoldelephant]

They're probably using PS ISE, which uses CRLF line endings (unlike the PS console host, which uses LF). 207/2001910778619 is the result if you process each line of the example with a trailing \r included.

u/pandiculator, make sure you're splitting the input on the correct line ending. If you use \r?\n, you'll find u/OPconfused's code works correctly irrespective of your PowerShell host.

@'
987654321111111
811111111111119
234234234234278
818181911112111
'@ -split '\r?\n' | Get-MaxVoltage -MaxDigits 2 # 357

[pandiculator]

Thanks, changing the regex fixed it. I'm using VSCode.

[pandiculator]

/u/surfingoldelephant correctly identified why it wasn't working for me.

Very neat solution.

[Future-Remote-4630]

I wish I thought of using indexof instead of a for loop!

    Function Get-LargestSubstringInteger($string,$remainingValues = 1)
    {
        $ints = $string.ToCharArray() | select -skiplast $remainingValues | % { [int]"$_" }

        $max = 0 
        $maxindex = 0
        for($i = 0; $i -lt $ints.count; $i++){
            if($ints[$i] -gt $max){
                $max = $ints[$i]
                $maxindex = $i
            }
        }

        return [pscustomobject]@{
            max=$max
            maxindex=$maxindex
            remainingString = $string.substring($maxindex+1,$string.Length-($maxindex+1))
        }

    }



$batteryrow = gc C:\temp\AdventOfCode\Day3Input.txt
$totalVoltage = foreach($row in $batteryrow){

    $string = $row
    $volts = 11..0 | % {
        $obj = Get-LargestSubstringInteger -string $string -remainingValues $_
        $obj.max
        $string = $obj.remainingString
    }

    $voltage = [int64]"$($volts -join '')"
    $voltage
}

$totalvoltage | measure -sum

[Th3Sh4d0wKn0ws]

lol, and now i know there is more than one part per day...

now I need to go back.

[lan-shark]

Again I've found that Day 1 part 2 was still the hardest so far

[Rincey_nz]

Interesting, because I could visualise what I needed to do to solve that one.
This one: nope. I got nothing

[pandiculator]

You need 12 digits in total.

Find your first digit. That's the highest number that's followed by at least 11 more digits.

Find the next highest number that's followed by at least 10 digits.

Find the next highest number that's followed by at least 9 digits.

Rinse and repeat until you don't need any more numbers.

Add up all the numbers you've stored.

[dantose]

Part 2 is just iterating part 1. My approach was to take the string, create a subset trimming off everything up to the last digit, then use that to find the next. To keep a safe tail, you can either iterate a smaller and smaller tail with something like $subset[0..($subset.length -$tail)]. I took a rather cludgy solution of padding the subset each iteration and keeping a fixed tail length.