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 Summary

Constructors

Constructor and Description
FrontMiddleBackQueue()

Method Summary

Modifier and Type	Method and 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 Detail

FrontMiddleBackQueue

public FrontMiddleBackQueue()

Method Detail

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()