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Queue using Stacks

Certification: Basic Level Accuracy: 0% Submissions: 0 Points: 5

Write a C program to implement a queue using two stacks. A queue is a FIFO (First-In-First-Out) data structure, while a stack is a LIFO (Last-In-First-Out) data structure. Your task is to implement a queue using only stack data structures and their standard operations (push, pop, peek, empty).

Example 1
    
  
  • Input: Operations = ["MyQueue", "push", "push", "peek", "pop", "empty"], Values = [[], [1], [2], [], [], []]
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  • Output: [null, null, null, 1, 1, false]
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  • Explanation: MyQueue myQueue = new MyQueue(); // Initialize queue
    
    myQueue.push(1); // Queue: [1]
    
    myQueue.push(2); // Queue: [1, 2]
    
    myQueue.peek(); // Return 1, queue: [1, 2]
    
    myQueue.pop(); // Return 1, queue: [2]
    
    myQueue.empty(); // Return false, queue: [2]
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Example 2
    
  
  • Input: Operations = ["MyQueue", "push", "pop", "empty"], Values = [[], [5], [], []]
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  • Output: [null, null, 5, true]
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  • Explanation: MyQueue myQueue = new MyQueue(); // Initialize queue
    
    myQueue.push(5); // Queue: [5]
    
    myQueue.pop(); // Return 5, queue: []
    
    myQueue.empty(); // Return true, queue: []
    •
Constraints
    
  
  • Use only standard stack operations (push, pop, peek, isEmpty)
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  • All operations must be valid (for example, no pop or peek operations will be called on an empty queue)
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  • 1 ≤ number of operations ≤ 100
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  • 1 ≤ values pushed to queue ≤ 100
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  • At most 100 calls will be made to push, pop, peek, and empty
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  • Time Complexity: O(1) amortized for all operations
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  • Space Complexity: O(n), where n is the number of elements in the queue
    •
QueueStackKPMGD. E. Shaw
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Hint
Solution

Solution Hints

    
  
  • Use two stacks: one for pushing elements (input stack) and one for popping elements (output stack)
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  • Push operation: Simply push the element onto the input stack
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  • Pop operation: If the output stack is empty, transfer all elements from the input stack to the output stack, then pop from the output stack
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  • Peek operation: Similar to pop, but return the top element of the output stack without removing it
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  • Empty operation: Check if both stacks are empty
    •

Steps to solve by this approach:

 Step 1: Create two stacks: inputStack for enqueue operations and outputStack for dequeue operations.

 Step 2: For the push operation, simply add the element to the inputStack.

 Step 3: For peek and pop operations, check if the outputStack is empty.

 Step 4: If the outputStack is empty, transfer all elements from inputStack to outputStack, which reverses their order.

 Step 5: For pop, return and remove the top element from the outputStack. 
 Step 6: For peek, return the top element from the outputStack without removing it.

 Step 7: The queue is empty when both stacks are empty.

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