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Stack Using Queues

Certification: Advanced Level Accuracy: 100% Submissions: 1 Points: 8

Write a C# program to implement a stack using only queues. Your implementation should support the standard stack operations: push, pop, top, and isEmpty.

Example 1
    
  
  • Input: push(1), push(2), top(), pop(), top(), isEmpty()
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  • Output: 2, 2, 1, false
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  • Explanation: 
    
      
      
    • After pushing 1 and 2, the top is 2.
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    • After popping, 2 is removed and the top becomes 1.
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    • The stack is not empty.
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Example 2
    
  
  • Input: push(3), pop(), isEmpty(), pop()
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  • Output: 3, true, Exception: Stack is empty
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  • Explanation: 
    
      
      
    • After pushing 3 and popping it, the stack becomes empty.
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    • Trying to pop from an empty stack should throw an exception.
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Constraints
    
  
  • You must use only standard queue operations: enqueue, dequeue, peek, isEmpty
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  • You cannot use any built-in stack implementation
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  • All operations must run in O(1) time complexity for pop and top, and O(n) for push
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  • Space Complexity: O(n)
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QueueStackTutorialspointTech Mahindra
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Hint
Solution

Solution Hints

    
  
  • Use two queues to implement the stack
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  • Make sure new elements are always at the front of one of your queues
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  • When pushing, move all elements from the first queue to the second queue
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  • Add the new element, then move all elements back
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  • For pop and top, just work with the front of the queue
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Steps to solve by this approach:

 Step 1: Use two queues to implement the stack functionality.
 Step 2: For push operation, move all elements from queue1 to queue2 temporarily.
 Step 3: Add the new element to the now-empty queue1, so it's at the front.
 Step 4: Move all elements back from queue2 to queue1.
 Step 5: For pop and top operations, work with the front of queue1 directly.
 Step 6: The isEmpty operation simply checks if queue1 is empty.
 Step 7: This approach ensures the most recently added element is always at the front of queue1.

Submitted Code :