(MEDIUM) Given a ciphertext String and an ArrayList of 26 key Strings, decrypt the characters in the ciphertext by finding the key containing each character and replacing it with the letter at the key's index (if the key at index 0 contains the character, the plaintext letter is 'A', and so forth).

Postcondition: The output String will be made of uppercase letters and spaces only - and because spaces are not encrypted by this algorithm, you know that the substitution keys cannot contain spaces either.