1. What is Coding‑Decoding?

Coding / Decoding – Quick Revision Notes (JKSSB – Social Forestry Worker Exam)

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1. What is Coding‑Decoding?

• Purpose: Test your ability to detect the rule (or “code”) that transforms a given set of symbols/letters/numbers into another set, and then apply the same rule to new data.
• Core Idea: Every coding problem has a consistent logical pattern. Identify it → apply it → get answer.

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2. General Strategy (3‑Step Checklist)

Step	Action	Why it helps
1. Observe	Look at the given coded pair(s). Note any change in length, order, case, symbols, numbers.	Gives clues about the type of operation (shift, reverse, substitution, etc.).
2. Hypothesize	Form a tentative rule (e.g., each letter → +2, each number → square, symbol → its keyboard neighbour).	Narrows down possibilities.
3. Verify & Apply	Test the rule on all given examples. If it works every time, apply it to the query. If not, modify the hypothesis.	Prevents careless mistakes.

Tip: If more than one rule fits the first example, test it on the second before deciding.

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3. Frequently Encountered Coding Types

Coding Type	Typical Transformation	Example (Input → Output)	Key Point to Remember
Alphabetic Shift	Each letter moved a fixed number of places forward/backward in the alphabet (wrap‑around allowed).	CAT → ECV ( +2 )	Remember A=1, B=2 … Z=26; use modulo 26.
Alphabetic Reverse	Letter replaced by its counterpart from the opposite end (A↔Z, B↔Y, …).	DOG → WLT	Think “Mirror”: position = 27‑original.
Letter‑Number Substitution	Letter → its alphabetical position (or vice‑versa). Number → letter of same position.	B → 2, 14 → N	Keep a quick A‑Z table handy (see below).
Vowel/Consonant Swap	Vowels replaced by next vowel (a→e, e→i, i→o, o→u, u→a) ; consonants shifted or unchanged.	BEA → CFI (B→C, E→F? actually E→F is +1, but we may also treat vowel shift)	Identify if only vowels or only consonants are affected.
Symbol Coding	Each symbol replaced by another symbol according to a fixed map (often keyboard adjacency or mirror).	@ → #, $ → % (shift right on QWERTY)	Visualise the keyboard or a given symbol‑code table.
Number Coding	Arithmetic operation on each digit or whole number (add, subtract, multiply, square, cube, digit‑sum, etc.).	123 → 6 (digit‑sum) or 5 → 25 (square)	Look for patterns like sum of digits, product, difference, square/cube.
Mixed Letter‑Number Coding	Combine two of the above (e.g., letter→number then shift).	ACE → 135 → 246 (letter→pos, then +1 each digit)	Break the problem into sub‑steps; solve each sequentially.
Position‑Based Coding	Output depends on the position of the character in the word (odd/even, prime index, etc.).	Apple → aPpLe (odd positions lower‑case, even upper‑case)	Track index (starting from 1) and apply rule conditionally.
Reverse Order	Entire string written backwards before/after other transformations.	CODE → EDOC (plain reverse) or CODE → GFQF (reverse then +2)	Always check if the length stays same; reversal is a common first/last step.
Binary / ASCII Coding	Letter → its ASCII/ binary value (or vice‑versa).	A → 65 (decimal) or 01000001 (binary)	Useful only when numbers look like 65, 66, etc.; remember A=65.
Symbol‑Shift (Keyboard)	Each symbol replaced by the key immediately to its right/left (or up/down) on QWERTY.	; → . (right shift)	Memorise the top row: ~!@#$%^&*()_+ etc. for quick reference.
Rotational Cipher (Caesar)	Same as alphabetic shift but often with a key given in the problem (e.g., ROT13).	HELLO → URYYB (ROT13)	If a number is mentioned (e.g., “shift by 5”), treat it as Caesar.
Cross‑Type Coding	Two different coding schemes applied to different parts (e.g., first half alphabetic shift, second half number coding).	AB12 → CD34 (AB→+2, 12→+2 each digit)	Split the string logically; apply separate rules.

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4. Handy Reference Tables

4.1 Alphabet ↔ Number (A=1 … Z=26)

Letter	No.	Letter	No.
A	1	N	14
B	2	O	15
C	3	P	16
D	4	Q	17
E	5	R	18
F	6	S	19
G	7	T	20
H	8	U	21
I	9	V	22
J	10	W	23
K	11	X	24
L	12	Y	25
M	13	Z	26

Tip: To find the reverse letter quickly: Reverse = 27 – Original.

4.2 Common Symbol‑Shift Maps (QWERTY)

Original	Right‑Shift	Left‑Shift
(space)	–	–
!	@	–
@	#	!
#	$	@
$	%	#
%	^	$
^	&	%
&		^
	(	&
(	)	*
)	_	(
_	+	)
+	–	_
… (continue similarly for other rows)

Memorise: Shift right = next key on the same row; Shift left = previous key.

4.3 Vowel Cycle (a→e→i→o→u→a)

Vowel	Next
a	e
e	i
i	o
o	u
u	a

Consonant shift (if required) usually follows the same +1 or +2 rule as normal letters, but always verify from examples.

4.4 Digit Manipulation Cheat‑Sheet | Operation | Result on a single digit d | Example |

———–	—————————–	———
+n (mod 10)	(d + n) % 10	7+4 → 1
–n (mod 10)	(d – n +10) % 10	3–5 → 8
×n (mod 10)	(d × n) % 10	6×3 → 8
Square (d²)	d² (may be 2‑digit)	4→16
Cube (d³)	d³	2→8
Digit‑sum	Σ digits of d (if d>9, repeat)	18→1+8=9
Complement to 9	9‑d	5→4

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5. Mnemonics & Memory Aids

Concept	Mnemonic	How to Use
Alphabet positions	“A = 1, Z = 26 – Think ‘A to Z’”	Recall quickly; for reverse use 27‑X.
Caesar shift	“Shift by the key, wrap like a clock”	Imagine a clock with 26 hours; add key, if >26 subtract 26.
Reverse alphabet	“Mirror in the middle (M ↔ N)”	Visualise the alphabet folded; A↔Z, B↔Y, … M↔N.
Vowel cycle	“AEIOU – Always Eat Ice‑cream Under Umbrella”	Helps recall the order a→e→i→o→u.
Symbol right‑shift	“Right‑hand rule: push the key to your right”	Picture your right finger moving one key right.
Digit‑sum → 9	“If it adds to 9, you’re divine”	Quick check for divisibility by 9; useful when code yields digit‑sum 9.
Odd/Even position	“Odd = Out, Even = Inside”	Odd positions often get a different treatment (e.g., upper‑case).
Binary to letter	“65 is ‘A’, add 1 for each next letter”	Memorise 65=A, 66=B … 90=Z.
Square/cube detection	“If result looks like a perfect square/cube, check power”**	16,25,36… are squares; 8,27,64… cubes.

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6. Step‑by‑Step Solved Examples #### Example 1 – Simple Alphabetic Shift

Code: FGHI → JKLM

Find: WXYZ → ?

Solution: 1. Observe: each letter moved +2 (F→H? actually F→J is +4? Let’s recalc: F→J (+4), G→K (+4), H→L (+4), I→M (+4)). So shift +4.

1. Apply +4 to WXYZ:

• W (+4) → A (wrap: W→X→Y→Z→A)
• X → B
• Y → C
• Z → D

Answer: ABCD

Example 2 – Reverse Alphabet + Shift

Code: MIND → NLME (given)

Find: ZERO → ?

Solution:

1. Test: M→N (+1), I→L (+3), N→M (–1), D→E (+1). Not uniform.
2. Try reverse then +1:

• Reverse of MIND = DNIM
• Apply +1: D→E, N→O, I→J, M→N → E O J N (doesn’t match).

1. Try +1 then reverse:

• MIND +1 = NJOE
• Reverse = EOJN (still not).

1. Look at given: M→N (+1), I→L (+3), N→M (–1), D→E (+1). Pattern +1, +3, –1, +1 repeating? Check length 4: positions 1,2,3,4 get +1,+3,–1,+1.
2. Apply same to ZERO:

• Z (pos1) +1 → A
• E (pos2) +3 → H – R (pos3) –1 → Q
• O (pos4) +1 → P

Answer: AHQP

(If the pattern didn’t fit, you would try other combos; the key is to test each hypothesis on all given pairs.)

Example 3 – Letter‑Number Conversion + Digit‑Sum

Code: B2 → 4 , D5 → 1

Find: F7 → ? Solution:

1. B→2 (letter→position), 2 stays 2 → combine? 2+2=4 → output 4.
2. D→4, 5 stays → 4+5=9 → digit‑sum of 9 = 9? but output is 1. Let’s try another: maybe multiply? B(2)×2=4 → matches first. D(4)×5=20 → digit‑sum 2+0=2 not 1.
3. Try add then digit‑sum:

• B(2)+2=4 → digit‑sum 4 → 4 (matches).
• D(4)+5=9 → digit‑sum 9 → 9 (not 1).

1. Try (letter position) – (number):

• B(2)-2=0 → maybe treat 0 as 10? no.

1. Look at outputs: 4 and 1. Notice 4 is 2², 1 is 1². Could be (letter position – number)²?

• B: 2-2=0 → 0²=0 not 4.
• D: 4-5=-1 → (-1)²=1 matches second! First fails. 6. Try (letter position + number)² then digit‑sum:
• B: (2+2)=4 → 4²=16 → digit‑sum 1+6=7 not 4.

1. Let’s brute think: maybe code is (letter position) × (number) then take last digit:

• B: 2×2=4 → last digit 4 ✔
• D: 4×5=20 → last digit 0 not 1. 8. Try (letter position) + (number) then take last digit:
• B: 2+2=4 → last digit 4 ✔
• D: 4+5=9 → last digit 9 not 1.

1. Try (letter position) ^ (number) (exponential) mod 10:

• B: 2²=4 mod10=4 ✔
• D: 4⁵=1024 mod10=4 not 1.

Given time, assume the intended pattern is (letter position) + (number) → if result >9, subtract 9 (i.e., modulo 9).

• B: 2+2=4 (<9) → 4 ✔
• D: 4+5=9 → 9-9=0? but output 1. Not working.

Takeaway: When stuck, write down all simple operations (add, sub, mul, mod, digit‑sum, square) and see which fits both examples. In exam, if none fits, re‑examine the given pair for possible typographical error or consider that the code might be position of letter in the word (not alphabet).

For revision purposes, remember the checklist:

• Letter→number (A=1…)
• Number→letter
• Simple arithmetic (+,−,×,÷)
• Digit‑sum / product
• Square / cube
• Modulo 9 or 10
• Combine two steps (e.g., letter→number then shift).

Example 4 – Symbol Coding (Keyboard Shift)

Code: @ # $ → # $ % Find: & * ( → ?

Solution:

• Each symbol shifted right by one key on the same row.
• Apply:
• & → * (right)
• * → ( (right)
• ( → ) (right)

Answer: * ( )

Example 5 – Mixed Letter‑Number with Position Dependency

Code: A1B2 → B2C3

Find: Z9Y8 → ?

Solution:

• Observe: each letter incremented by +1 (A→B, B→C).
• Each number incremented by +1 (1→2, 2→3).
• Apply to Z9Y8:
• Z→A (wrap)
• 9→0 (wrap)
• Y→Z
• 8→9 Answer: A0Z9 —

7. Common Pitfalls & How to Avoid Them

Pitfall	Why it Happens	Remedy
Assuming a single operation when two are used	Early letters/numbers look consistent; later ones break the pattern.	Always test the hypothesis on all given pairs before finalizing.
Forgetting wrap‑around (mod 26 or mod 10)	Shifts near the end of alphabet/digit set give unexpected results.	After adding/subtracting, apply modulo (if ≥26 subtract 26; if ≥10 subtract 10).
Mixing up 0‑based vs 1‑based indexing	A=0 in programming, but A=1 in reasoning.	Remember the exam uses A=1. When in doubt, test both; only one will fit the examples.
Overlooking case changes	Some codes change lower‑case to upper‑case or vice‑versa.	Check if output letters are all uppercase/lowercase or mixed; note any case flip as part of rule.
Ignoring symbol rows	Symbol shift may move to a different row (e.g., from bottom row to top row).	Visualise the keyboard; a shift may be up/down as well as left/right.
Misreading the direction of shift	+2 vs –2 can give same result for a small sample but diverge later.	Determine direction by comparing first and last letters of a pair (e.g., A→C is +2, C→A is –2).
Assuming symmetry	Thinking reverse of a rule is the same as the rule itself.	Verify symmetry by applying the rule twice; if you don’t get original, it’s not symmetric.
Skipping digit‑sum step	Many number codes reduce to a single digit via repeated addition.	If output is a single digit (<10) while inputs are multi‑digit, suspect digit‑sum or modulo 9.

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8. Quick Reference Cheat‑Sheet (One‑Page)

ALPHABET
A=1 … Z=26               Reverse = 27‑X
Shift:   X → (X+K) mod 26 (if 0→26)
ROT13:   +13 (A↔N, B↔O …)

NUMBER
Digit‑sum: repeat until <10
Mod 9:   n % 9 (0→9)
Mod 10:  n % 10
Square:  n²
Cube:    n³
Add/Mul: (n±k) mod 10, (n×k) mod 10

VOWEL CYCLEa→e→i→o→u→a

SYMBOL (QWERTY) RIGHT SHIFT
!@#$%^&()_+   →   @#$%^&()_+?
(hold Shift for top row)

CASE
UPPER ↔ lower : toggle case
(often used with shift)

POSITION BASED
Odd index → +1, Even index → –1   (or vice‑versa)
Prime index → square, Composite → digit‑sum

MIXED STEP1️⃣ Letter → number (A=1…)
2️⃣ Apply arithmetic on numbers
3️⃣ Number → letter (if needed)

Keep this sheet handy; glance at it before each coding question.

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9. Practice Drill (5 Mini‑Questions)

#	Given Code	Find	Hint
1	GHJK → ILMN	STUV → ?	Look for uniform shift.
2	MOP → NQP	XYZ → ?	Check if only middle letter changes.
3	5$9 → 6%0	3#7 → ?	Symbol shift? Number shift?
4	A1C3 → B2D4	Z9Y8 → ?	Letter +1, Number +1.
5	&(@ → $)%(	!@# → ?*	Determine direction of symbol move.

Answers (for self‑check):

1. TUVW (shift +2 each letter)
2. XZA (first & last unchanged, middle +1)
3. 4@8 (each symbol right‑shift, each number +1)
4. A0Z9 (letter +1 with wrap, number +1 with wrap)
5. “$%&”` (each symbol left‑shift)

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10. Final Revision Tips

1. Start with the simplest explanation – usually a shift of +1 or –1.
2. If the first guess fails, write down two alternative rules (e.g., shift +2 and reverse) and test them on the second example.
3. Use the elimination method – rule out operations that clearly don’t fit (e.g., if output contains a symbol not present in input, a pure letter‑shift is impossible).
4. Time management: allocate ~45 seconds per coding problem; if stuck >20 seconds, move on and return later if time permits.
5. Stay calm: the pattern is always logical; panic leads to overlooking obvious shifts.

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You are now equipped with a solid, step‑by‑step toolkit for tackling any Coding/Decoding question in the JKSSB Social Forestry Worker exam. Revise the tables, run through the mnemonics, and practice a few problems daily – you’ll see your accuracy and speed improve dramatically. Good luck!