Package g1601_1700.s1670_design_front_middle_back_queue

Class FrontMiddleBackQueue

  • All Implemented Interfaces:
    
public final class FrontMiddleBackQueue

    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:

    • <code>1 <= val <= 10<sup>9</sup></code>

    • At most 1000 calls will be made to pushFront, pushMiddle, pushBack, popFront, popMiddle, and popBack.

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