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Stack

Introduction​

A stack is a linear data structure that follows the Last-In, First-Out (LIFO) principle. The last element added is the first one to be removed.

Key Operations​

  • Push: Add an element to the top of the stack (O(1))
  • Pop: Remove the top element from the stack (O(1))
  • Peek/Top: View the top element without removing it (O(1))
  • IsEmpty: Check if the stack is empty

Example (Python)​

stack = []

# Push elements
stack.append(10)
stack.append(20)
stack.append(30)

# Peek at the top
print(stack[-1])  # Output: 30

# Pop elements
print(stack.pop())  # Output: 30
print(stack.pop())  # Output: 20

# Check if empty
if not stack:
    print("Stack is empty!")

Applications​

  • Function call management (call stack)
  • Undo/redo features in editors
  • Expression evaluation (postfix, prefix)
  • Syntax parsing

When to Use a Stack​

  • When you need to reverse data
  • When you need to track nested or recursive operations

Limitations​

  • Only the top element is accessible
  • Not suitable for random access
  • Queue: Follows First-In, First-Out (FIFO)
  • Deque: Double-ended queue, allows insertion/removal from both ends