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 java.lang.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 Summary

    Constructors
    Constructor
    Description
    MyStack()
     

  • Method Summary

    Modifier and Type
    Method
    Description
    boolean
    empty()
     
    int
    pop()
     
    void
    push(int x)
     
    int
    top()
     

    Methods inherited from class java.lang.Object

    clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

  • 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()