题目

Design your implementation of the circular queue. The circular queue is a linear data structure in which the operations are performed based on FIFO (First In First Out) principle and the last position is connected back to the first position to make a circle. It is also called “Ring Buffer”.

One of the benefits of the circular queue is that we can make use of the spaces in front of the queue. In a normal queue, once the queue becomes full, we cannot insert the next element even if there is a space in front of the queue. But using the circular queue, we can use the space to store new values.

Your implementation should support following operations:

• MyCircularQueue(k): Constructor, set the size of the queue to be k.
• Front: Get the front item from the queue. If the queue is empty, return -1.
• Rear: Get the last item from the queue. If the queue is empty, return -1.
• enQueue(value): Insert an element into the circular queue. Return true if the operation is successful.
• deQueue(): Delete an element from the circular queue. Return true if the operation is successful.
• isEmpty(): Checks whether the circular queue is empty or not.
• isFull(): Checks whether the circular queue is full or not.

Example:

MyCircularQueue circularQueue = new MyCircularQueue(3); // set the size to be 3
circularQueue.enQueue(1);  // return true
circularQueue.enQueue(2);  // return true
circularQueue.enQueue(3);  // return true
circularQueue.enQueue(4);  // return false, the queue is full
circularQueue.Rear();  // return 3
circularQueue.isFull();  // return true
circularQueue.deQueue();  // return true
circularQueue.enQueue(4);  // return true
circularQueue.Rear();  // return 4

Note:

• All values will be in the range of [0, 1000].
• The number of operations will be in the range of [1, 1000].
• Please do not use the built-in Queue library.

用一个定长数组

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|-----        <- 实际窗口
---->|

代码

class MyCircularQueue {

private int[] table;
private int size, head, curr;
private boolean isFull, isEmpty;

/** Initialize your data structure here. Set the size of the queue to be k. */
public MyCircularQueue(int k) {
table = new int[k];
size = k;
curr = 0;
isFull = (k == 0)? true : false;
isEmpty = true;
}

/** Insert an element into the circular queue. Return true if the operation is successful. */
public boolean enQueue(int value) {
if (!isFull()) {
table[curr++] = value;
curr %= size;
if (curr == head) isFull = true;
isEmpty = false;
return true;
} else {
return false;
}
}

/** Delete an element from the circular queue. Return true if the operation is successful. */
public boolean deQueue() {
if (!isEmpty()) {
if (curr == head) isEmpty = true;
isFull = false;
return true;
} else {
return false;
}
}

/** Get the front item from the queue. */
public int Front() {
if (isEmpty()) return -1;
}

/** Get the last item from the queue. */
public int Rear() {
if (isEmpty()) return -1;
int last = (curr - 1 + size) % size;
return table[last];
}

/** Checks whether the circular queue is empty or not. */
public boolean isEmpty() {
return isEmpty;
}

/** Checks whether the circular queue is full or not. */
public boolean isFull() {
return isFull;
}
}

/**
* Your MyCircularQueue object will be instantiated and called as such:
* MyCircularQueue obj = new MyCircularQueue(k);
* boolean param_1 = obj.enQueue(value);
* boolean param_2 = obj.deQueue();
* int param_3 = obj.Front();
* int param_4 = obj.Rear();
* boolean param_5 = obj.isEmpty();
* boolean param_6 = obj.isFull();
*/

结果 