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  1. import java.util.Stack;
  2. /**
  3.  * Implement Queue operations using two stacks
  4.  * @author Prateek
  5.  */
  6.  class QueueQWithStacks  {
  7.  
  8. 	private Stack<Integer> stack1 = new Stack<Integer>(); // for enqeue operations
  9. 	private Stack<Integer> stack2 = new Stack<Integer>();
  10.  
  11. 	/**
  12. 	 * Enqueue Operation
  13. 	 * @throws InterruptedException : to given delay between operations so that it prints on console
  14. 	 */
  15. 	public void enqueue(Integer item) throws InterruptedException {
  16. 		Thread.sleep(10);
  17. 		System.out.println("Enqueue: " + item);
  18. 		stack1.push(item);
  19. 	}
  20.  
  21. 	/**
  22. 	 * Dequeue Operation
  23. 	 * @return FIFO element
  24. 	 */
  25. 	public Integer dequeue() throws InterruptedException {
  26. 		Thread.sleep(10);
  27. 		if(stack2.isEmpty())
  28. 		{
  29. 			if(!stack1.isEmpty())
  30. 			{
  31. 				while(!stack1.isEmpty())
  32. 				{
  33. 					stack2.push(stack1.pop());
  34. 				}
  35. 			}
  36. 			else
  37. 			{
  38. 				System.out.println("Stack is Empty");
  39. 				return -1;
  40. 			}
  41. 		}
  42. 		int item=stack2.pop();
  43. 		System.out.println("Dequeue: " + item);
  44. 		return item;
  45. 	}
  46.  
  47. 	public static void main(String[] args) throws InterruptedException {
  48. 		QueueQWithStacks obj=new QueueQWithStacks();
  49. 		obj.enqueue(1);
  50. 		obj.enqueue(2);
  51. 		obj.enqueue(3);
  52. 		obj.dequeue();
  53. 		obj.dequeue();
  54. 		obj.dequeue();
  55. 		obj.dequeue();
  56. 		obj.enqueue(4);
  57. 		obj.enqueue(5);
  58. 		obj.enqueue(6);
  59. 		obj.enqueue(7);
  60. 		obj.dequeue();
  61. 		obj.dequeue();
  62. 		obj.dequeue();
  63. 		obj.dequeue();
  64. 		obj.dequeue();
  65. 	}
  66. }
  67.  
Success #stdin #stdout 0.08s 380160KB
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Standard input is empty
stdout
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Enqueue: 1
Enqueue: 2
Enqueue: 3
Dequeue: 1
Dequeue: 2
Dequeue: 3
Stack is Empty
Enqueue: 4
Enqueue: 5
Enqueue: 6
Enqueue: 7
Dequeue: 4
Dequeue: 5
Dequeue: 6
Dequeue: 7
Stack is Empty
https://ideone.com/egp7Vz
Queue with two Stacks
language:
Java (HotSpot 12)
created:
10 years ago
visibility:
public

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