Package g0201_0300.s0232_implement_queue_using_stacks

Class MyQueue

java.lang.Object
g0201_0300.s0232_implement_queue_using_stacks.MyQueue
public class MyQueue extends java.lang.Object
232 - Implement Queue using Stacks.

Easy

Implement a first in first out (FIFO) queue using only two stacks. The implemented queue should support all the functions of a normal queue (push, peek, pop, and empty).

Implement the MyQueue class:

  • void push(int x) Pushes element x to the back of the queue.
  • int pop() Removes the element from the front of the queue and returns it.
  • int peek() Returns the element at the front of the queue.
  • boolean empty() Returns true if the queue is empty, false otherwise.

Notes:

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

Example 1:

Input:

 ["MyQueue", "push", "push", "peek", "pop", "empty"]
 [ [], [1], [2], [], [], []]

Output:

 [null, null, null, 1, 1, false]

Explanation:

 MyQueue myQueue = new MyQueue();
 myQueue.push(1); // queue is: [1]
 myQueue.push(2); // queue is: [1, 2] (leftmost is front of the queue)
 myQueue.peek(); // return 1
 myQueue.pop(); // return 1, queue is [2]
 myQueue.empty(); // return false

Constraints:

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

Follow-up: Can you implement the queue such that each operation is amortized O(1) time complexity? In other words, performing n operations will take overall O(n) time even if one of those operations may take longer.

  • Constructor Summary

    Constructors
    Constructor
    Description
    MyQueue()
     

  • Method Summary

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

    Methods inherited from class java.lang.Object

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

  • Constructor Details

    • MyQueue

      public MyQueue()

  • Method Details

    • push

      public void push(int x)

    • pop

      public int pop()

    • peek

      public int peek()

    • empty

      public boolean empty()