![]() ![]() 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. Return "[ " + this.rollNo + ", " + this.Difficulty: Easy, Asked-in: Microsoft, Amazon, Adobe it will return true after removing last student from deque As ArrayDeque is modified it is printed to check if last student object is removed or not. We're creating an ArrayDeque of Student, adding some elements, print it and then use removeLast() method to get the a last student removed. The following example shows the usage of Java ArrayDeque removeLast() method with Student objects. As ArrayDeque is modified it is printed to check if last element is removed or not. We're creating an ArrayDeque of String, adding some elements, print it and then use removeLast() method to get the last element. The following example shows the usage of Java ArrayDeque removeLast() method with Strings. Let us compile and run the above program, this will produce the following result − let us print all the elements available in deque again ("Retrieved Element is = " + deque.removeLast()) it will retrieve last element after removing from deque let us print all the elements available in deque ![]() use add() method to add elements in the deque We're creating an ArrayDeque of Integers, adding some elements, print it and then use removeLast() method to get the last element. The following example shows the usage of Java ArrayDeque removeLast() method with Integers. NoSuchElementException − if this deque is empty. This method returns the tail (last element) of this deque. Declarationįollowing is the declaration for () method This operation modifies the ArrayDeque instance. The Java ArrayDeque removeLast() method retrieves and removes the last element of this deque. ![]()
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