CRYPTO4  The Bytelandian Cryptographer (Act IV)
The Bytelandian Cryptographer has been requested by the BBFO to put forward an encryption scheme which would allow the BBFO to communicate with its foreign associates. After some intensive studies, he has decided upon the Vigenďż˝re cipher. Messages written using 26 upper case characters of the Latin alphabet: A, B, ..., Z which are interpreted as integers 0,1, ..., 25 respectively. The secret cypher for transmitting a message is known to both sides and consists of n integers k_{1}, k_{2},...,k_{n}. Using this cypher, the ith number x_{i} of the input message x is encrypted to the form of the ith number of the output message y, as follows:
y_{i} =(x_{i}+k_{1+ ((i1) mod n)}) mod 26.
You are trying to find out the content of a message transmitted by the BBFO. By a lucky stroke of fortune, your spies managed to intercept the message in both its plaintext and encrypted form (x and y respectively). Unfortunately, during their dramatic escape the files they were carrying where pierced by bullets and fragments of messages x and y were inadvertently lost. Or were they? It is your task to reconstruct as much of message x as you possibly can.
Input
The first line of input contains a single integer t<=200 denoting the number of test cases. t test case descriptions follow.
For each test case, the first line contains one integer m which is some upper bound on the length of the cypher (1<=n<=m<=100000). The second line of input contains the original message x, while the third line contains the encrypted message y. The messages are expressed using characters 'A''Z' (interpreted as integers 025) and '*' (denoting a single character illegible due to damage). The total length of the input file is not more than 2MB.
Output
For each test case output a single line containing the original message x, with asterisks '*' in place of only those characters whose value cannot be determined.
Example
Input: 4 1 A*X*C **CM* 4 *B***A AAAAAA 6 *B***A AAAAAA 4 *AA******* AAAAAAAAAA Output: A*XHC *BA*BA *B***A *AA**A****Warning: large Input/Output data, be careful with certain languages.
The time limit is strict for this problem.
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Prabhat Kumar Gupta:
20110531 10:39:24
WHAT CAN BE MAX SIZE OF MESSAGE Last edit: 20110531 12:40:35 

pittacus:
20101019 07:22:32
4


naraysln:
20100914 11:17:28
Finally solved it after 58 trials... :D 

[Trichromatic] XilinX:
20091015 15:31:54
Read the problem statement CAREFULLY! 
Added by:  Konrad Piwakowski 
Date:  20041116 
Time limit:  17s 
Source limit:  50000B 
Memory limit:  1536MB 
Cluster:  Cube (Intel G860) 
Languages:  All except: NODEJS PERL6 VB.NET 
Resource:  DASM Programming League 2004 (problemset 3) 