Coding & Decoding - Cheat Sheet
Your last-minute revision companion for mastering coding and decoding patterns in the CSE Subprofessional exam.
Basic Mechanics
Formulas
Letter Position: A=1, B=2, C=3... Z=26
Meaning
Standard alphabetical numbering system
Watch out
Don't confuse O (15th letter) with 0 (zero)
When to use
When codes involve position substitution
Reverse Alphabet: A↔Z, B↔Y, C↔X... (positions sum to 27)
Meaning
Mirror alphabet pairing system
Watch out
M and N are self-paired in some systems
When to use
When letters are replaced by their mirror opposite
Shift Formula: New Position = (Old Position + Shift) mod 26
Meaning
Mathematical representation of Caesar cipher
Watch out
Remember wraparound: Z+1 becomes A, not AA
When to use
For consistent letter shifting with wraparound
Common values
Value
1
Symbol
A
Quantity
Letter A position
Value
26
Symbol
Z
Quantity
Letter Z position
Value
M=13, N=14
Symbol
M,N
Quantity
Middle letters
Important facts
- Most CSE patterns use single, consistent rules
- Letter position memorization speeds up solving
- Wraparound occurs when shifts exceed Z or go before A
- Number coding often uses arithmetic operations
- Hybrid patterns combine 2+ simple rules
Key definitions
Coding
Example
CAT → DBU using +1 shift
Applying a rule to convert plaintext into coded form
Decoding
Example
DBU → CAT using -1 shift
Reversing the coding rule to recover original text
Caesar Shift
Example
HELLO → IFMMP (+1 shift)
Moving each letter forward/backward by fixed positions
Mirror Coding
Example
CAT → XZG (C→X, A→Z, T→G)
Replacing letters with their alphabet reverse
Diagrams to know
- Alphabet with position numbers (A=1 to Z=26)
- Reverse alphabet mapping chart
- Shift pattern examples for +1, +2, +3
Common Coding Patterns
Common values
Value
+1, +2, +3, -1, -2
Symbol
±n
Quantity
Common shifts
Value
A, E, I, O, U
Symbol
V
Quantity
Vowels
Value
E=5, J=10, O=15, T=20
Symbol
landmarks
Quantity
Key positions
Important facts
- Shift patterns are most common in CSE exams
- Position coding uses A=1, B=2... Z=26 system
- Reversal coding simply flips the string
- Group coding applies different rules to different letter types
- Number sequences follow arithmetic or geometric patterns
Key definitions
Letter Shift
Example
DOG → EPH (+1 each)
Each letter advances/retreats by fixed positions
Position Substitution
Example
CAB → 3-1-2
Replace letters with their numerical positions
String Reversal
Example
WORLD → DLROW
Write the entire word backwards
Group Coding
Example
Vowels +1, Consonants +2
Different rules for vowels vs consonants
Diagrams to know
- Shift pattern visualization
- Reverse alphabet correspondence table
Decoding Strategy
Important facts
- Compare corresponding letters position by position
- Calculate difference between original and coded letters
- Look for constant differences (shift patterns)
- Check for reversal if no clear shift pattern
- Test rule on all given examples before applying
Key definitions
Pattern Recognition
Example
LEMON→MFNPO shows +1 shift pattern
Identifying the rule by comparing coded and original pairs
Rule Testing
Example
Test +1 rule on second word pair
Verifying discovered pattern on multiple examples
Diagrams to know
- Step-by-step decoding flowchart
- Letter comparison alignment method
Number Coding
Formulas
Square Pattern: n → n²
Meaning
Each number becomes its square
Watch out
Distinguish from doubling (n → 2n)
When to use
When coded numbers are perfect squares
Arithmetic Sequence: n → n + d
Meaning
Add constant difference to each term
Watch out
Don't assume +1 without checking other terms
When to use
When differences between terms are constant
Geometric Sequence: n → n × r
Meaning
Multiply by constant ratio
Watch out
Check if it's addition or multiplication pattern
When to use
When ratios between terms are constant
Common values
Value
1,4,9,16,25,36,49,64,81,100
Symbol
n²
Quantity
Perfect squares 1-10
Value
2,4,8,16,32,64
Symbol
2ⁿ
Quantity
Powers of 2
Important facts
- Number patterns often use basic arithmetic operations
- Squaring is common in CSE number coding
- Check for addition vs multiplication patterns
- Powers and roots may appear in advanced items
- Sequence patterns follow mathematical progressions
Key definitions
Squaring Pattern
Example
3→9, 5→25, 7→49
Each number becomes its square value
Doubling Pattern
Example
2→4, 3→6, 5→10
Each number multiplied by 2
Power Pattern
Example
2→8, 3→27 (cubing pattern)
Numbers raised to consistent power
Diagrams to know
- Common number pattern examples
- Arithmetic vs geometric sequence identification
Must remember
- A=1, B=2... Z=26 (memorize key positions: E=5, J=10, O=15, T=20, Y=25)
- Most common pattern: consistent letter shift (+1, +2, -1, -2)
- Reverse alphabet pairs sum to 27 (A+Z=27, B+Y=27, etc.)
- Always test your discovered rule on ALL given examples
- Wraparound rule: after Z comes A, before A comes Z
- Number coding often uses squaring (n→n²) or doubling (n→2n)
- String reversal = write the word completely backwards
- Position substitution replaces each letter with its alphabet number
- Check for group coding (vowels vs consonants have different rules)
- CSE prefers single, clean rules over complex combinations
Last minute tips
- Write A-Z with numbers 1-26 on scratch paper before starting
- For shifts, count on your fingers if needed - accuracy over speed initially
- If no obvious shift, check for alphabet reversal (A↔Z pattern)
- Number patterns: try squaring first, then doubling, then adding
- Don't overthink - CSE uses straightforward patterns, not complex combinations
Comparison tables
Coding Pattern Types
| Pattern Type | Rule | Example | Recognition Clue |
|---|---|---|---|
| Letter Shift | Each letter ±n positions | CAT→DBU (+1) | Constant position difference |
| Reverse Alphabet | A↔Z, B↔Y, etc. | CAT→XZG | Letter pairs sum to 27 |
| Position Substitution | Letters become numbers | CAB→3-1-2 | Numbers match positions |
| String Reversal | Write backwards | HELLO→OLLEH | Same letters, reverse order |
Number vs Letter Coding
| Aspect | Letter Coding | Number Coding |
|---|---|---|
| Common Operations | Shift, Reverse, Substitute | Square, Add, Multiply |
| Pattern Recognition | Compare letter positions | Calculate arithmetic relationships |
| Difficulty Level | Moderate (26 letters) | Easier (simple math) |
Diagrams
Coding & Decoding Pattern Overview
Comprehensive overview of all coding and decoding patterns commonly tested in CSE Subprofessional exams
Decoding Strategy Process
Step-by-step flowchart for systematically identifying and applying coding patterns in exam questions
Pattern Recognition Timeline
Chronological approach to systematically test for different coding patterns, from most to least common