2017 Advent of Code - day 2

2017-adventofcode2.ps1

$in = @'
5 9 2 8
9 4 7 3
3 8 6 5
'@ -split "`r?`n"

$in | ForEach-Object { 

# part 1 was easy, split string, measure the max and min, then find the difference
# part 1 #    $minmax = -split $_ | Measure-Object -Minimum -Maximum
# part 1 #    $minmax.Maximum - $minmax.Minimum

# part 2 was harder, needed a couple of redesigns
# concerned that one input might be a trap and the "evenly divisible" numbers
# might be 1,N or N,N, so didn't go for "work out the divisors" and avoided
# testing numbers against themselves.
# make the test include forwards and backwards check.

    $rowNums = -split $_ | ForEach-Object { [int]$_ }

    $a, $b = foreach ($i in 0..($rowNums.Length-1)) {
        foreach ($j in 0..($rowNums.Length-1)) {
            if ($i -ne $j)
            {
                $x,$y = $rowNums[$i,$j]
                if ((($x/$y) -eq [int]($x/$y)) -or (($y/$x) -eq [int]($y/$x)))
                {
                    $x
                }
            }
        }
    }

    $min, $max = $a, $b | Sort-Object
    $max / $min

} | Measure-Object -Sum | Select-Object -ExpandProperty sum