Package g0201_0300.s0225_implement_stack_using_queues

Class MyStack

java.lang.Object
g0201_0300.s0225_implement_stack_using_queues.MyStack
public class MyStack extends Object
225 - Implement Stack using Queues.

Easy

Implement a last-in-first-out (LIFO) stack using only two queues. The implemented stack should support all the functions of a normal stack (push, top, pop, and empty).

Implement the MyStack class:

  • void push(int x) Pushes element x to the top of the stack.
  • int pop() Removes the element on the top of the stack and returns it.
  • int top() Returns the element on the top of the stack.
  • boolean empty() Returns true if the stack is empty, false otherwise.

Notes:

  • You must use only standard operations of a queue, which means that only push to back, peek/pop from front, size and is empty operations are valid.
  • Depending on your language, the queue may not be supported natively. You may simulate a queue using a list or deque (double-ended queue) as long as you use only a queue’s standard operations.

Example 1:

Input [“MyStack”, “push”, “push”, “top”, “pop”, “empty”] [[], [1], [2], [], [], []]

Output: [null, null, null, 2, 2, false]

Explanation:

 MyStack myStack = new MyStack();
 myStack.push(1);
 myStack.push(2);
 myStack.top(); // return 2
 myStack.pop(); // return 2
 myStack.empty(); // return False

Constraints:

  • 1 <= x <= 9
  • At most 100 calls will be made to push, pop, top, and empty.
  • All the calls to pop and top are valid.

Follow-up: Can you implement the stack using only one queue?

  • Constructor Details

    • MyStack

      public MyStack()

  • Method Details

    • push

      public void push(int x)

    • pop

      public int pop()

    • top

      public int top()

    • empty

      public boolean empty()