What is Stack (LIFO, Operations, Applications)

Stack Data Structure: Complete Guide in Hindi

Stack एक बहुत ही fundamental (बुनियादी) और linear (रेखीय) Data Structure है, जिसका मतलब है कि इसमें data elements एक sequence (श्रृंखला) में store होते हैं।

Stack की सबसे बड़ी पहचान यह है कि इसमें data daalne (insertion) aur data nikalne (deletion) ka kaam sirf ek hi end se hota hai, jise hum Top (शीर्ष) kehte hain.

LIFO Principle (LIFO सिद्धांत)

Stack ka execution, yaani kaam karne ka tareeka, LIFO principle par based hai.

  • LIFO ka full form hai: Last In, First Out
  • Matlab Kya Hai?: Iska seedha matlab yeh hai ki woh element (तत्व) jo stack mein sabse aakhir (last) mein daala gaya tha, woh hi element stack se sabse pehle (first) nikala jaayega.

Simple Analogy (उदाहरण):

Aap ek sikkaon ka dher (pile of coins) imagine kijiye. Jab aap naya sikka dalte hain, toh woh hamesha top par jaata hai (Last In). Jab aap sikka nikalte hain, toh aap hamesha sabse upar wala sikka hi nikalte hain (First Out).

LIFO Analogy: Pile of Coins

Stack Operations (स्टैक ऑपरेशंस)

Stack mein mukhya roop se (primarily) teen operations hote hain, jo hamesha stack ke Top par hi perform hote hain:

A. Basic Operations

1. Push (डालना)

  • Kaam: Stack mein top par ek naya item dalne (insert karne) ka operation.
  • Mechanism: Jab Push hota hai, toh Top pointer ek position upar chala jaata hai aur naya item us position par rakh diya jaata hai.
  • Condition: Agar stack poora bhara hua hai (yani usmein aur jagah nahi hai), toh is situation ko Stack Overflow kehte hain, aur Push operation nahi ho sakta.
Push Operation in Stack

2. Pop (निकालना)

  • Kaam: Stack ke top se item ko bahar nikalne (remove karne) ka operation.
  • Mechanism: Jab Pop hota hai, toh top item ko return (waapas) kiya jaata hai, aur Top pointer ek position neeche (down) ho jaata hai.
  • Condition: Agar stack khaali hai (yani usmein koi item nahi hai), toh is situation ko Stack Underflow kehte hain, aur Pop operation nahi ho sakta.
Pop Operation in Stack

B. Auxiliary Operations

3. Peek / Top (देखना)

  • Kaam: Stack ke Top par kaunsa item hai, use dekhne (access karne) ka operation, lekin use hataane (remove karne) ke bina.
  • Benefit: Isse hum Top item ko check kar sakte hain, bina Stack ke structure ko badle.
Peek Operation in Stack

4. IsEmpty (खाली है?)

  • Kaam: Check karna ki kya stack mein koi item nahi hai.
  • Benefit: Yeh Underflow hone se pehle checking karne ke liye zaroori hai.
IsEmpty Operation in Stack

5. IsFull (भरा है?)

  • Kaam: Check karna ki kya stack mein aur jagah nahi hai (agar stack fixed size ka ho).
  • Benefit: Yeh Overflow hone se pehle checking karne ke liye zaroori hai.
IsFull Operation in Stack

Stack Applications (स्टैक के अनुप्रयोग)

Stack ka use Computer Science aur Programming mein bahut saari important cheezon ko manage karne ke liye hota hai:

1. Function Call Management (कॉल स्टैक)

  • Jab bhi koi program chalta hai aur ek function doosre function ko call karta hai, toh woh execution order ek special stack mein manage hota hai jise Call Stack kehte hain.
  • Har function call ki jaankari (return address, local variables, etc.) ko push kiya jaata hai. Jab function khatam hota hai, toh uski jaankari ko pop kar liya jaata hai. LIFO hi ensure karta hai ki control sahi jagah par wapas jaaye.
Call Stack Application

2. Expression Conversion and Evaluation (अभिव्यक्ति का मूल्यांकन)

  • Use: Infix expressions (jaise A + B * C) ko Postfix (Reverse Polish Notation) ya Prefix (Polish Notation) mein convert karne ke liye.
  • Why Stack? Stack operator precedence (operators ki priority) ko track karta hai aur brackets ko manage karta hai, jisse expressions ka evaluation (मूल्यांकन) sahi order mein ho pata hai.

3. Undo / Redo Mechanism (अंडू / रीडू तंत्र)

  • Text editors (Jaise MS Word) aur graphic software mein undo aur redo options Stack ki madad se kaam karte hain.
  • Har action (jaise typing, deleting) ko Undo Stack mein push kiya jaata hai. Jab aap Undo karte hain, toh action pop hota hai. Redo ke liye ek alag stack use hota hai.
Undo Redo Mechanism with Stack

4. Backtracking Algorithms (पीछे हटना एल्गोरिदम)

  • Use: Jab hamein saare possible paths (saare sambhav raste) explore karne hote hain (Jaise Sudoku solve karna ya Maze-solving).
  • Jab hum ek raste par aage badhte hain, toh hum state ko push karte hain. Agar woh rasta galat (dead end) nikla, toh hum pop karke pichle sahi raste par wapas (backtrack) jaate hain.
Backtracking with Stack

5. Recursion (रिकर्शन)

  • Jab ek function khud ko baar-baar call karta hai (Recursion), toh internally yeh process Call Stack ka hi use karti hai.
Recursion using Stack

नोट: यह ब्लॉग पोस्ट Stack Data Structure को आसानी से समझाने के लिए बनाया गया है। अगर आप और जानना चाहते हैं, तो कमेंट करें!

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