Package g1601_1700.s1670_design_front_middle_back_queue

Class FrontMiddleBackQueue

java.lang.Object
g1601_1700.s1670_design_front_middle_back_queue.FrontMiddleBackQueue
public class FrontMiddleBackQueue extends java.lang.Object
1670 - Design Front Middle Back Queue.

Medium

Design a queue that supports push and pop operations in the front, middle, and back.

Implement the FrontMiddleBack class:

  • FrontMiddleBack() Initializes the queue.
  • void pushFront(int val) Adds val to the front of the queue.
  • void pushMiddle(int val) Adds val to the middle of the queue.
  • void pushBack(int val) Adds val to the back of the queue.
  • int popFront() Removes the front element of the queue and returns it. If the queue is empty, return -1.
  • int popMiddle() Removes the middle element of the queue and returns it. If the queue is empty, return -1.
  • int popBack() Removes the back element of the queue and returns it. If the queue is empty, return -1.

Notice that when there are two middle position choices, the operation is performed on the frontmost middle position choice. For example:

  • Pushing 6 into the middle of [1, 2, 3, 4, 5] results in [1, 2, 6, 3, 4, 5].
  • Popping the middle from [1, 2, 3, 4, 5, 6] returns 3 and results in [1, 2, 4, 5, 6].

Example 1:

Input: [“FrontMiddleBackQueue”, “pushFront”, “pushBack”, “pushMiddle”, “pushMiddle”, “popFront”, “popMiddle”, “popMiddle”, “popBack”, “popFront”]

[ [], [1], [2], [3], [4], [], [], [], [], []]

Output: [null, null, null, null, null, 1, 3, 4, 2, -1]

Explanation:

 FrontMiddleBackQueue q = new FrontMiddleBackQueue(); q.pushFront(1); // [1]
 q.pushBack(2); // [1, 2]
 q.pushMiddle(3); // [1, 3, 2]
 q.pushMiddle(4); // [1, 4, 3, 2]
 q.popFront(); // return 1 -> [4, 3, 2]
 q.popMiddle(); // return 3 -> [4, 2]
 q.popMiddle(); // return 4 -> [2]
 q.popBack(); // return 2 -> []
 q.popFront(); // return -1 -> [] (The queue is empty)

Constraints:

  • 1 <= val <= 109
  • At most 1000 calls will be made to pushFront, pushMiddle, pushBack, popFront, popMiddle, and popBack.

  • Constructor Summary

    Constructors
    Constructor
    Description
    FrontMiddleBackQueue()
     

  • Method Summary

    Modifier and Type
    Method
    Description
    int
    popBack()
     
    int
    popFront()
     
    int
    popMiddle()
     
    void
    pushBack(int val)
     
    void
    pushFront(int val)
     
    void
    pushMiddle(int val)
     

    Methods inherited from class java.lang.Object

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

  • Constructor Details

    • FrontMiddleBackQueue

      public FrontMiddleBackQueue()

  • Method Details

    • pushFront

      public void pushFront(int val)

    • pushMiddle

      public void pushMiddle(int val)

    • pushBack

      public void pushBack(int val)

    • popFront

      public int popFront()

    • popMiddle

      public int popMiddle()

    • popBack

      public int popBack()