Exercise: Reverse any letters of the input string

Get-ReverseString.ps1

function Get-ReversedString {
<#
.SYNOPSIS
    Reverse any letters of the input string
.EXAMPLE
    Get-ReversedString '!abc123def456!'
    # returns: !cba123fed456!
#>
[OutputType([string])]
[CmdletBinding()]
param (
    [Parameter(Mandatory,ValueFromPipeline)]
    [string]$InputString
)
function ReverseList($List){$List.Reverse() ; $List ; $List.Clear()}

$CharArray = [char[]]$InputString
$TempList  = [Collections.Generic.List[char]]::new()
$TempChars = 0..($CharArray.Length-1) | foreach {
    $ThisChar   = $CharArray[$_]
    $IsNotEmpty = $TempList.Count -gt 0
    $IsChar     = [char]::IsLetter($ThisChar)
    $LastChar   = $_ -eq $CharArray.Length-1

    if     ($IsChar)     {$TempList.Add($ThisChar)}
    elseif ($IsNotEmpty) {ReverseList $TempList}
    
    # reverse once more at the end if it's not empty
    if ($LastChar -and $IsNotEmpty) {ReverseList $TempList}
}
Write-Verbose "Temp array: $($TempChars -join $null)"
$i = 0
$ReversedArray = $CharArray | foreach {
    $IsChar = [char]::IsLetter($_)
    if ($IsChar) {$TempChars[$i] ; $i++}
    else         {$_}
}
$ReversedString = [string]::Join($null,$ReversedArray)

Write-Output $ReversedString
}


# alternative way:
Function Get-ReversedString ([string]$InputString) {
    $Find = [Regex]::Matches($InputString,'[a-zA-Z]+').Value
    $Temp = -join ($Find | ForEach {-join $_[($_.Length-1)..0]})

    $i = 0
    ([char[]]$InputString | foreach {
        $IsChar = [char]::IsLetter($_)
        if ($IsChar) {$Temp[$i] ; $i++}
        else         {$_}
    }) -join $null
}


# another take:

Function Get-ReversedString {
<#
.SYNOPSIS
    Reverse any letters of the input string
.EXAMPLE
    Get-ReversedString '!abc123def456!'
    # returns: !cba123fed456!
#>
[OutputType([string])]
[CmdletBinding()]
param (
    [Parameter(Mandatory,ValueFromPipeline)]
    [string]$InputString
)
$Find = [Regex]::Matches($InputString,'[a-zA-Z]+').Value
$Temp = -join $Find.ForEach({-join $_[($_.Length-1)..0]})

$i = 0
$ReversedArray = [char[]]$InputString | foreach {
    if ([Char]::IsLetter($_)) {$Temp[$i] ; $i++}
    else                      {$_}
}
Write-Output (-join $ReversedArray)
}


# and finally for PS7+ (using the ternary operator)

Function Get-ReversedString {
<#
.SYNOPSIS
    Reverse any letters of the input string
.EXAMPLE
    '!abc123def456!' | Get-ReversedString
    # returns: !cba123fed456!
#>
#Requires -Version 7.0
[OutputType([string])]
[CmdletBinding()]
param (
    [Parameter(Mandatory,ValueFromPipeline)]
    [Alias('InputString')]
    [string]$In
)
$Find = [Regex]::Matches($In,'[a-zA-Z]+').Value
$Temp = -join $Find.ForEach({-join $_[($_.Length-1)..0]})
Write-Verbose "Temporary string: $Temp"
$i = 0
-join ([char[]]$In).ForEach({[Char]::IsLetter($_) ? $($Temp[$i];$i++) : $_})
}