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 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 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()