Overview
Stack LIFO structure hai — last in, first out. Python list se easily implement hota hai.
Analogy
Jaise plate stack — upar se plate lagate ho, upar se hi uthate ho.
Step-by-step
- stack = [] se empty stack banao
- stack.append(x) se push karo
- stack.pop() se pop karo (last element)
- stack[-1] se peek karo bina pop kiye
Visual
stack = []
stack.append(1) # [1]
stack.append(2) # [1, 2]
stack.pop() # 2, stack=[1]
Common mistakes
- Empty stack se pop() — IndexError
- List ka front (index 0) use karna — O(n) shift
- stack[-1] peek hai, stack.pop() remove karta hai
Practice questions
- Valid parentheses check karo stack se
- Undo functionality stack se simulate karo