This problem is taken from the Collegiate Challenge Finals.
Class Name: Vigenere
Method Name: coder
Parameters: String,String,int
Returns: String
The Vigenere Cipher is a simple but strong encryption algorithm. Unlike many
simple encryption algorithms, the Vigenere Cipher is immune to frequency
analysis because it alters the normal frequency by using more than one alphabet
to encrypt the message. Instead of there being a one-to-one relationship
between each letter and its substitute, there is a one-to-many relationship
between each letter and its substitute.
The Vigenere Cipher is based on the following table (which has a simple pattern
so you don't actually have to store the table).
A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
A A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
B B C D E F G H I J K L M N O P Q R S T U V W X Y Z A
C C D E F G H I J K L M N O P Q R S T U V W X Y Z A B
D D E F G H I J K L M N O P Q R S T U V W X Y Z A B C
. . . . .
. . . . .
. . . . .
When encoding a message with the Vigenere Cipher, a code word is written
repeatedly over the message. Each letter in the message is replaced with the
letter at the intersection of the row given by the corresponding code word
letter and the column given by the message letter.
Implement a class Vigenere that contains a method coder. The method encodes
and decodes Strings of capital letters (A-Z) using the Vigenere Cipher. coder
takes two Strings and an int as a parameter. The first String is the message.
The second String is the code word. The int specifies whether the message
should be encoded or decoded:
int=1: encode message
int=2: decode message
The method returns a String that is the resulting (encoded or decoded) message.
If the message or code word is not valid (They do not contain only capital
letters in the range A to Z, or the code word is of length 0) the method
returns "ERROR"
If the int is not 1 or 2, the method returns "ERROR"
If both the message and code word are of length 0, or if just the message has
length 0 (and the code word is valid), the method should return an empty string.
The method signature is:
public String coder(String message,String codeWord,int action);
message and codeWord are Strings with length less than 1000.
Examples:
If the message is "TOPCODERISGREAT" and the codeWord is "CODE" and the action
is encode (1), write the code word over the message and look up letters in the
table:
Code Word:
CODECODECODECOD
Message:
TOPCODERISGREAT
Encoded:
VCSGQRHVKGJVGOW
because the letter in row C column T is V,
the letter in row O column O is C,
etc....
If the message is "HRWCQYRORWSCGKUO" and the codeWord is "OK" and the action is
decode (2), the decoded message is "THISCODEDMESSAGE".
If the message is "HowAreYou" and the codeWord is "GO" and the action is encode
(1), the method returns "ERROR" because the message isn't all capital letters.
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