Advent of PowerShell 2018, Day 2

1.ps1

param(
  [string[]]$IDs
)

# Prepare our char count function
$TestCharExactCount = {
  return @($_.ToCharArray() |Group-Object -NoElement).Where({$_.Count -eq $n}).Count -gt 0
}

# Create two new closures over $n = 2 and $n = 3
$n = 2
$TestExactly2 = $TestCharExactCount.GetNewClosure()
$n = 3
$TestExactly3 = $TestCharExactCount.GetNewClosure()

# Count occurences
$2s = $IDs.Where($TestExactly2).Count
$3s = $IDs.Where($TestExactly3).Count

# Multiplly counts for final result
return $2s * $3s

2.ps1

param(
  [string[]]$IDs
)

:IDSearch
for($i = 0; $i -lt $IDs.Count - 1; $i++){
  for($j = $i + 1; $j -lt $IDs.Count; $j++){
    $HammingDistance = Get-HammingDistance -a $IDs[$i] -b $IDs[$j]
    if($HammingDistance -eq 1){
      $ID1,$ID2 = $IDs[$i,$j]
      break IDSearch
    }
  }
}

$sharedChars = for($charIdx = 0; $charIdx -lt $ID1.Length;$charIdx++){
  if($ID1[$charIdx] -eq $ID2[$charIdx]){
    $ID1[$charIdx]
  }
}

return -join $SharedChars