We dequeue the last remaining element in queue Q1 and store it in a variable called stackTop.In this loop, we dequeue each element from queue Q1 and enqueue it into queue Q2. Otherwise, we run a loop until there is only one element left in queue Q1. If queue Q1 is empty, we throw an error message "stack underflow" and return.To achieve this, we can follow the following steps. Implementation of the pop operationĪs previously mentioned, to perform the pop operation, our goal is to remove the last element inserted into queue Q1 using another queue, Q2. We are performing a constant number of operations i.e. After inserting the element, we increment the value of stackSize by 1 to track the current size of the stack. This means we insert the element x at the back of queue Q1, which will become the top element of the stack. To add a new element to the stack, we enqueue it to the first queue, Q1. We define methods for stack operations: void push(int x) and int pop().We declare a variable called stackSize to track the current size of the stack.We declare two queues, Q1 and Q2, to simulate stack operations.Suppose we define a class called StackUsingQueue to implement a stack using queues. Therefore, to perform the pop operation using a single queue, we need to use two queues. To do this, we can use an additional queue to store the removed elements. However, before removing the last element, we need to store and maintain the order of the removed elements for future use. This would mean removing all the elements in the queue except for the last element, which is the top element of the stack. One solution to this problem could be to continuously remove elements from the queue until we reach the element at the back. The key question here is: how do we remove the element at the back of the queue? But the queue is a first-in, first-out (FIFO) data structure, which means we can only remove elements from the front of the queue. However, if we want to perform a pop operation, we need to remove the last element inserted into the queue, which is at the back of the queue. In this case, we can perform a push operation by simply inserting the new element at the back of the queue. Suppose we use a single queue to implement a stack. This can be achieved by manipulating the order of the elements in the queue. Therefore, to simulate a stack using a queue, we need to keep track of the last element inserted and make sure that it is the first element to be deleted. In a stack, we insert and delete elements from one end only, but in a queue, we insert elements at the back and delete elements from the front. We can understand the basic idea for implementing a stack using a queue by considering the order of insertion and deletion in both data structures. Using two queues: O(n) pop operation and O(1) push operation Using a single queue: O(1) pop operation and O(n) push operation.Using two queues: O(1) pop operation and O(n) push operation.Using two queues: O(n) pop operation and O(1) push operation.We must use only standard queue operations.In contrast, the queue is a first-in-first-out (FIFO) data structure, in which elements are added from one end (back) and removed from the other end(front). Stack is a last-in-first-out (LIFO) data structure, in which elements are added and removed from the top end.int pop(): Remove an element from the top of the stack and return it.void push(int x): Insert an element x to the top of the stack.The implemented stack should support standard push(x) and pop() operations. Write a program to implement a stack using the queues. Key takeaway: An excellent problem to visualize the use case of stack and queue operations. Difficulty: Easy, Asked-in: Microsoft, Amazon, Adobe
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