Coding‑Decoding – Assam Police Constable (Reasoning Ability)
Goal – Learn how to recognise and apply pattern‑based coding/decoding in a short time.
1. Simple Explanation
| Term | What it means |
|---|---|
| Coding | Converting a given word/phrase into a coded form (e.g., “CAT” → “3”). |
| Decoding | Recovering the original word/phrase from its coded representation. |
Typical patterns:
- Alphabets → Numbers (A=1, B=2, …)
- Vowel/Consonant replacement
- Reversal (word or letters)
- Word‑to‑Word (e.g., “CAT” → “C+AT” → “C”).
- Syllable/Word‑segment coding (e.g., “COMPUTER” → “CO+MP+UT+ER”).
- Letter‑position (first/last letter, middle letter, etc.).
The key is to find a consistent rule that applies to all given examples.
2. Key Points to Remember
| # | Point | Why it Matters |
|---|---|---|
| 1 | Identify the pattern first | Answers will be correct only if pattern is recognised. |
| 2 | Look for hints in the problem statement | Often the type of coding is hinted (“vowels are replaced by numbers”). |
| 3 | Check all given pairs | Reduces ambiguity by providing multiple examples. |
| 4 | Use elimination | If a pattern fails for one pair, discard it and try another. |
| 5 | Practice mental math & quick letter mapping | Saves time in the exam. |
| 6 | Keep a cheat‑sheet | Note common patterns while studying for quick reference. |
| 7 | Be careful with “word to word” coding | The output may be a word, a letter, a number, or a mix. |
| 8 | Use “reverse engineering” | Try decoding first; it often shows the rule more clearly. |
3. Worked Example
Problem
| Code | Decoded Word |
|---|---|
| 3 | CAT |
| 5 | DOG |
| 4 | BIRD |
| 7 | FISH |
Find the rule and decode the word for the code 6.
Step‑by‑Step Solution
| Step | Action | Observation |
|---|---|---|
| 1 | List the coding pairs | 3→CAT, 5→DOG, 4→BIRD, 7→FISH |
| 2 | Count letters in each word | CAT=3, DOG=3, BIRD=4, FISH=4 |
| 3 | Compare code with letter count | Not equal. |
| 4 | Try vowel count | CAT=1, DOG=1, BIRD=1, FISH=1 → all 1, not useful. |
| 5 | Try consonant count | CAT=2, DOG=2, BIRD=3, FISH=3 → no pattern. |
| 6 | Try sum of alphabetical values | CAT=3+1+20=24, DOG=4+15+7=26, BIRD=2+9+18+4=33, FISH=6+9+19+8=42 → not matching. |
| 7 | Try difference between first and last letter | CAT: 3–20=‑17 → abs=17, DOG: 4–7=‑3 → abs=3. Not consistent. |
| 8 | Try “number of letters in the word of the code” | Code 3 → word “three” has 5 letters; but gives CAT. No. |
| 9 | Try “position of the word in alphabetically sorted list” | Unlikely. |
| 10 | Check “number of letters + number of vowels” | CAT: 3+1=4 (not 3). |
| 11 | Try “number of distinct letters” | CAT=3, DOG=3, BIRD=4, FISH=4 → matches the code! |
| 12 | Validate | All four pairs satisfy “code = number of distinct letters in the word”. |
| 13 | Decode code 6 | Need a word with 6 distinct letters. Examples: PLANT, GHOST (5) – we need 6 unique letters. |
| Possible answer: “BRIDGE” (B,R,I,D,G,E) → 6 distinct letters. | ||
| 14 | Answer | 6 → BRIDGE (or any other 6‑letter word with all distinct letters). |
Take‑away
- The coding rule was “Number of distinct letters in the word”.
- Always try simpler counts (letters, vowels, consonants) before moving to complex sums.
4. Quick Revision Summary
| Topic | Quick Tips |
|---|---|
| Recognising Patterns | • Count letters, vowels, consonants. • Check sums, differences, positions. • Look for “word‑to‑word” patterns. |
| Common Coding Types | 1. Alphabets → Numbers (A=1, B=2, …). 2. Vowels as 0/1. 3. Distinct‑letter count. 4. Reversal (output is reverse of input). 5. Word‑segment coding (e.g., “CAT” → “C+AT”). |
| Decoding Strategy | 1. Start with given pairs. 2. Try the simplest rule first. 3. Eliminate inconsistent rules. 4. Confirm with all pairs. 5. Apply to unknown. |