![]() 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
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