⭐ Sabse Important Points · एक नज़र में
- Alphabet Position: A=1, B=2, ..., Z=26; reverse position = 27 - forward position (A=26, Z=1).
- Direct Letter-to-Number Mapping: If a table or code is given, replace each letter with its assigned number/symbol exactly as shown.
- Constant Shift Rule: If each letter moves by the same number of places, apply the same shift to every letter of the new word.
- Position-Based Number Code: Sometimes the number represents the letter's position in the word (e.g., first letter = 1, second = 2) or alphabet position.
- Alternating Shift Rule: Check if shifts follow +n, -n or +1, +2, +3 pattern by comparing consecutive letters.
- Word Substitution: In sentence-based coding, a word is replaced by another word; identify the repeated word across sentences to decode.
Introduction · परिचय
Coding-Decoding is a reasoning topic where a word or number is coded using a specific rule, and you must either decode a given code or apply the same rule to a new word. In Delhi Police Constable exams, questions are usually based on letter shifting, letter-to-number mapping, or symbol substitution. The key is to identify the pattern quickly and apply it consistently.
Letter Shifting and Alphabet Position
Most coding-decoding questions use the English alphabet where A=1, B=2, ..., Z=26. In letter shifting, each letter of the word is moved forward or backward by a fixed number of places. Sometimes the shift alternates (e.g., +1, -1, +2, -2) or follows a pattern based on position. Always write the alphabet with positions to avoid mistakes.
- Write alphabet with positions
- Compare first letters of word and code
- Find shift (+/- n)
- Verify with second letter
- Apply same shift to target word
📐 Formula / Rule Box · सूत्र याद रखो
Reverse Alphabet Position
Reverse position = 27 - Forward position
Shift Rule
Coded letter position = Original position ± n
Constant Shift Rule
If each letter moves by the same number of places, apply the same shift to every letter of the new word.
Alternating Shift Rule
Check if shifts follow +n, -n or +1, +2, +3 pattern by comparing consecutive letters.
Opposite Letter Rule
Sometimes each letter is replaced by its opposite (A↔Z, B↔Y, etc.), i.e., position becomes 27 - original position.
⭐ Key Points · याद रखने वाली बातें
- Alphabet Position: A=1, B=2, ..., Z=26; reverse position = 27 - forward position (A=26, Z=1).
✍️ Solved Example 1 · हल किया हुआ उदाहरण
❓ Question: If CAT is coded as DBU, how is DOG coded?
✅ Solution: EPH
💡 Explanation: C→D (+1), A→B (+1), T→U (+1). So each letter shifts +1. D→E, O→P, G→H gives EPH.
✍️ Solved Example 2 · हल किया हुआ उदाहरण
❓ Question: If PEN is coded as QFO, how is BOOK coded?
✅ Solution: CPPL
💡 Explanation: P→Q (+1), E→F (+1), N→O (+1). Apply +1 to BOOK: B→C, O→P, O→P, K→L = CPPL.
Number Coding and Symbol Substitution
In number coding, letters are assigned numbers either by their alphabet position or by a fixed mapping given in the question. In symbol substitution, letters or words are replaced by symbols or other words according to a given code. The rule may be direct (same letter = same number/symbol) or positional (number depends on the letter's place in the word). Read the given code carefully and map each letter individually.
| Letter Shifting | Number/Symbol Coding |
|---|---|
| Rule based on alphabet position shift | Rule based on fixed mapping or position in word |
| Usually same shift for all letters | Each letter may have different number/symbol |
| Example: CAT→DBU (+1) | Example: ROSE→18-15-19-5 (alphabet position) |
⭐ Key Points · याद रखने वाली बातें
- Direct Letter-to-Number Mapping: If a table or code is given, replace each letter with its assigned number/symbol exactly as shown.
- Position-Based Number Code: Sometimes the number represents the letter's position in the word (e.g., first letter = 1, second = 2) or alphabet position.
- Word Substitution: In sentence-based coding, a word is replaced by another word; identify the repeated word across sentences to decode.
- Consistency Check: After decoding, verify the rule on all given examples before applying to the question.
✍️ Solved Example 1 · हल किया हुआ उदाहरण
❓ Question: If in a code language, 'pen' is written as '123', 'hen' as '423', and 'men' as '523', what is the code for 'ten'?
✅ Solution: 623
💡 Explanation: The last two letters 'en' are coded as '23' in all words. The first letter changes: p=1, h=4, m=5. So t should be 6 (following the pattern of increasing by 1 from 5). Hence 'ten' = 623.
✍️ Solved Example 2 · हल किया हुआ उदाहरण
❓ Question: If 'ROSE' is coded as 18-15-19-5, how is 'LILY' coded?
✅ Solution: 12-9-12-25
💡 Explanation: Each letter is replaced by its alphabet position: R=18, O=15, S=19, E=5. So L=12, I=9, L=12, Y=25.
Practice Questions · खुद हल करके देखो
पहले खुद try karo, phir “Answer dekho” dabakar check karo. 👇
Q1If 'TIGER' is coded as 'UJHFS', how is 'LION' coded?
👀 Answer dekho
✅ Answer: MJPO
💡 Explanation: Each letter shifts +1: T→U, I→J, G→H, E→F, R→S. Apply to LION: L→M, I→J, O→P, N→O = MJPO.
Q2In a certain code, 'BOOK' is written as 'CPPL'. How is 'PEN' written in that code?
👀 Answer dekho
✅ Answer: QFO
💡 Explanation: B→C (+1), O→P (+1), O→P (+1), K→L (+1). So P→Q, E→F, N→O = QFO.
Q3If 'SUN' is coded as 19-21-14, how is 'MOON' coded?
👀 Answer dekho
✅ Answer: 13-15-15-14
💡 Explanation: Letters are replaced by alphabet positions: S=19, U=21, N=14. So M=13, O=15, O=15, N=14.
⚠️ Common Mistakes · ये गलतियाँ बिल्कुल मत करना
- Assuming a constant shift without checking the second letter: always verify the pattern with at least two letters before applying.
- Forgetting reverse alphabet positions: remember A=26, Z=1 when opposite-letter coding is used.
- Mixing up position in word with alphabet position in number coding: read whether the number represents the letter's alphabet rank or its place in the word.
- Not re-checking the decoded word against all given examples: a rule that fits one example may not fit others.
⚡ Quick Revision · Exam से पहले 2 मिनट में दोहराओ
- Alphabet Positions: Memorize A=1 to Z=26 and reverse positions (A=26, Z=1) for quick shifting.
- Shift Verification: Confirm the shift using the first two letters of the given word-code pair before applying to the target word.
- Number Coding Check: First test alphabet-position coding; if it fails, look for a direct mapping table or position-in-word rule.
- Time Saver: In exams, eliminate options by decoding only the first letter of the target word.