Rating:
## Challenge
We get only 45 characters to convert the letters in a string into alternating upper and lower case:
```
"Hello World! Hallo Welt!"
```
becomes
```
"HeLlO wOrLd! HaLlO wElT!"
```
## Solution
A legit 44 character solution which works for all given input:
```perl
$_=lc"@ARGV";s/[a-z]/$u^=" ";$&^$u/ige;print
```
Explanation:
`$_=lc"@ARGV"` is just `$_ = lowercase("#{@ARGV}")`
`print` without argument defaults to `print($_)`
`s/[a-z]/$u^=" ";$&^$u/ige` is $_.gsub!(/[a-z]/)
`$u^=" ";` means switch $u betwen ascii character 0 and ascii character 32 (space) every iteration
`$&^$u` xors with 32, which just so happens to be difference between ascii uppercase and lowercase chars
**flag{chosingaflagisthemostdifficultpart}**
## Notes
The challenge creator had some interesting comments for us [here](https://github.com/teamavidya/ctf/commit/52f5789e743af94c147d4e5e0fd3796bc162872b#commitcomment-13953040)
Bogbert commented that he had found a 34 character solution!!
```perl
print pop=~s/\pL/lc$&^($u^=$")/ger
```
## Solved by
taw
