Stacks

Stacks follow LIFO (Last In First Out) principle. Elements are added and removed from the top.

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Base

Initial stack: [10, 20, 30] - Top: 30, Base: 10

javascript

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// Stack Implementation using Array
class Stack {
  constructor() {
    this.items = [];
  }
  // Push element onto stack
  push(element) {
    this.items.push(element);
  }
  // Pop element from stack
  pop() {
    if (this.isEmpty()) {
      return "Stack is empty";
    }
    return this.items.pop();
  }
  // Peek at top element
  peek() {
    if (this.isEmpty()) {
      return "Stack is empty";
    }
    return this.items[this.items.length - 1];
  }
  // Check if stack is empty
  isEmpty() {
    return this.items.length === 0;
  }
  // Get stack size
  size() {
    return this.items.length;
  }
  // Time Complexity:
  // Push: O(1)
  // Pop: O(1)
  // Peek: O(1)
  // Search: O(n)

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Explanation

Stacks are linear data structures that follow the LIFO principle. They're used in expression evaluation, function call management, and undo operations. All main operations (push, pop, peek) are O(1).

Operations & Complexity

PushO(1)

Add element to top

PopO(1)

Remove element from top

PeekO(1)

View top element

SearchO(n)

Must traverse stack

Time Complexity