#P16994. [NWERC 2018] Kleptography
[NWERC 2018] Kleptography
Problem Description
John likes simple ciphers. He had been using the “Caesar” cipher to encrypt his diary until recently, when he learned a hard lesson about its strength by catching his sister Mary browsing through the diary without any problems.
Rapidly searching for an alternative, John found the famous “Autokey” cipher. He uses a version that takes the lower-case letters a--z and internally translates them in alphabetical order to the numbers to .
The encryption key begins with a secret prefix of letters. Each of the remaining letters of the key is copied from the letters of the plaintext , so that for . Encryption of the plaintext to the ciphertext follows the formula .
Mary was able to get a peek at the last letters John typed before he noticed her, encrypted the text document, and left. This could be her chance.
Input Format
The input consists of:
- One line with two integers and (, ), where is the keyword length as well as the number of letters Mary saw, and is the length of the text.
- One line with lower-case letters, the last letters of the plaintext.
- One line with lower-case letters, the whole ciphertext.
Output Format
Output the plaintext of John's diary.
5 16
again
pirpumsemoystoal
marywasnosyagain
1 12
d
fzvfkdocukfu
shortkeyword