Coding and Decoding
Encode and decode using rule-based patterns
Coding and decoding questions hide a word, number or symbol behind a rule and ask you to apply or reverse that rule. The rule may shift alphabet positions, substitute symbols, reverse or rearrange positions, or combine more than one operation. Treat each given example as a constraint, derive one consistent mapping and verify it on every character before answering.
Key formulas and rules
Key concepts
Start with a representation
Write A to Z with their positions when the code uses letters. For numerical codes, make a letter-to-number table. For symbols, align the source and coded words character by character. This turns a visual puzzle into a set of small constraints.
Uniform alphabet shifts
In a Caesar-style shift, every letter moves by the same number of positions and wraps around after Z. A shift of +1 maps A to B and Z to A. Confirm the shift with at least two pairs before applying it to the target word.
Substitution and repeated letters
A substitution code assigns a replacement to each source letter. In a simple fixed mapping, the same source letter must receive the same replacement every time. Repeated letters are a useful check: if the source has two identical letters, the coded word should show the corresponding repeated code unless the question states that position changes the rule.
Reversal and transposition
Some codes change positions rather than letter values. Check whether the word is reversed, split into blocks, or rearranged by a fixed position pattern. Write position numbers above the word and track where each character moves. Do not describe a transformation as a letter shift when it is actually a rearrangement.