Class FrontMiddleBackQueue
- java.lang.Object
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- g1601_1700.s1670_design_front_middle_back_queue.FrontMiddleBackQueue
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public class FrontMiddleBackQueue extends Object
1670 - Design Front Middle Back Queue.Medium
Design a queue that supports
push
andpop
operations in the front, middle, and back.Implement the
FrontMiddleBack
class:FrontMiddleBack()
Initializes the queue.void pushFront(int val)
Addsval
to the front of the queue.void pushMiddle(int val)
Addsval
to the middle of the queue.void pushBack(int val)
Addsval
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]
returns3
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 topushFront
,pushMiddle
,pushBack
,popFront
,popMiddle
, andpopBack
.
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Constructor Summary
Constructors Constructor Description FrontMiddleBackQueue()
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Method Summary
All Methods Instance Methods Concrete Methods Modifier and Type Method Description int
popBack()
int
popFront()
int
popMiddle()
void
pushBack(int val)
void
pushFront(int val)
void
pushMiddle(int val)
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