(HARD) Given a String ciphertext and a keyword of length n, decrypt the columnar transposition cipher described at the following page:

https://en.wikipedia.org/wiki/Transposition_cipher#Columnar_transposition

Note that this is the irregular version with no "filler" letters to complete the rectangle if it is not completely filled. It is quite possible that the last row of plaintext, therefore, will be a different length than the other rows. Having unequal length rows also makes for an additional challenge writing the columns into the output.

The first test case uses only letters for plaintext and key, but actually, in theory, this cipher can function with any visible characters.