EncryptedMessage | Topcoder Archive

Problem Statement

Wireless devices are extremely vulnerable to unauthorized access. The information sent between wireless devices can be easily intercepted. To protect some private information the following encoding method may be used. For each chunk of the conversation, a secret String key is chosen. The key will have the same length as the chunk of the conversation, represented by message.
To find the i^th character of the encoded message, we take the i^th characters of key and message (lets call them k_i and m_i respectively). First we determine whether the resulting character will be upper- or lower- case. It will be lower-case only if exactly one of k_i and m_i is lower-case, and upper-case otherwise. Then we calculate the 0-based index of the character in the alphabet, which is equal to the sum of the 0-based indices of k_i and m_i modulo 26. For example, if key = "Key" and message = "ABc", the encoded message will be "KfA".

Given two Strings, key and message, return the encoded message.

Definition

Class:: EncryptedMessage
Method:: createMessage
Parameters:: String, String
Returns:: String
Method signature:: String createMessage(String key, String message)
(be sure your method is public)

Constraints

key and message will be the same length.
key and message will contain between 1 and 50 characters, inclusive.
key and message will contain only letters ('a'-'z', 'A'-'Z').

Examples

```
"Key"
```
```
"ABc"
```
```
Returns: "KfA"
```
'A' has index 0, and k0 and m0 are both uppercase, hence the first character of the encoded message is an uppercase 'K'. k1 is lowercase, while m1 is uppercase, making the second encoded character lowercase. Since 'B' has index 1, and 'e' has index 4, the resulting character has index 5, which is 'f'. The last character will be uppercase, and has an index of (24+2)%26 = 0, making it an 'A'.
```
"ABcd"
```
```
"dcBA"
```
```
Returns: "dddd"
```
```
"ZZZZZZZ"
```
```
"aaaaaaa"
```
```
Returns: "zzzzzzz"
```

"AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA"

"TheQuickBrownFoxJumpsOverTheLazyDog"

Returns: "TheQuickBrownFoxJumpsOverTheLazyDog"

An 'A' in the key leaves the corresponding character in message unchanged.

"qfHEFqKrcXICJAruXuqpdmVINqkZYl"

"YKtWshAgTuFhXeJkBxsRhwfdMmfTek"

Returns: "opaAxXKXvrNjGeaEYRIgKIalZCPScV"

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