Stack and Queue

Stack & Queue in DSA (Java)

Understand LIFO & FIFO structures for efficient problem solving.

📌 Topics Covered

1. Stack
2. Queue
3. Java Implementation
4. Important Questions

📚 Stack (LIFO)

Stack follows Last In First Out principle.

💡 Last inserted element is removed first.

Operations

• Push
• Pop
• Peek
• isEmpty

Applications

• Expression evaluation
• Undo/Redo
• Function call stack

🚶 Queue (FIFO)

Queue follows First In First Out principle.

💡 First inserted element is removed first.

Operations

• Enqueue
• Dequeue
• Front

Applications

• Process scheduling
• Printer queue
• BFS traversal

☕ Java Implementation

class Stack { int[] arr; int top = -1; void push(int x) { arr[++top] = x; } int pop() { return arr[top--]; } }

🧪 Important Questions

1. Stack vs Queue difference
2. Implement stack using queue
3. Time complexity (O(1))
4. Applications in real-world

🎯 Conclusion

Stacks and queues are fundamental data structures used in many real-world systems and interview problems.