Coding-Decoding

• Understand letter-shifting codes (e.g., each letter replaced by another a fixed number of positions away).
• Decode word/number substitution codes based on a given pattern.
• Apply the discovered pattern/rule to encode or decode a new word.

1. In a simple letter-shift code, each letter of the alphabet is replaced by the letter a fixed number of positions ahead or behind (e.g., A→D means shift +3).
2. To decode, find the pattern by comparing the given word and its code letter by letter.
3. Number codes may assign each letter a number based on its position in the alphabet (A=1, B=2, ... Z=26).
4. Some codes use a reversal pattern (first letter matches last, etc.) — always check multiple possibilities.

If CAT is coded as DBU, what is the code for DOG?

C->D (+1), A->B (+1), T->U (+1). Each letter shifts forward by 1.
D->E, O->P, G->H
So DOG is coded as EPH.

• Assuming the shift amount without verifying it against every letter in the example.
• Forgetting that the alphabet wraps around (Z+1 = A) in some coding schemes.
• Not checking if the code could instead be a reversal or number-based pattern.

• If BOOK is coded as CPPL, what is the shift rule?
• If DOG = 4-15-7 (using A=1...Z=26), what would CAT be?

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