# LeetCode – Design Circular Queue

## 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.

## 实现：

``````typedef struct {
int *value;
int tail;
int size;
int cnt;

} MyCircularQueue;
bool myCircularQueueIsEmpty(MyCircularQueue* obj) ;
bool myCircularQueueIsFull(MyCircularQueue* obj);

/** Initialize your data structure here. Set the size of the queue to be k. */

MyCircularQueue* myCircularQueueCreate(int k) {
MyCircularQueue* obj;

if (k == 0){
return NULL;
}
obj = (MyCircularQueue*)malloc(sizeof(MyCircularQueue));
obj->value = (int*)malloc(sizeof(int)*k);
obj->size=k;
obj->tail=-1;
obj->cnt=0;
return obj;
}

/** Insert an element into the circular queue. Return true if the operation is successful. */
bool myCircularQueueEnQueue(MyCircularQueue* obj, int value) {
if (!myCircularQueueIsFull(obj)){
obj->tail = (obj->tail+1) % obj->size;
obj->value[obj->tail]= value;
obj->cnt += 1;
return true;
}
else{
return false;
}
}

/** Delete an element from the circular queue. Return true if the operation is successful. */
bool myCircularQueueDeQueue(MyCircularQueue* obj) {
if (myCircularQueueIsEmpty(obj)){
return false;
}
else {
obj->cnt -= 1;
return true;
}
}

/** Get the front item from the queue. */
int myCircularQueueFront(MyCircularQueue* obj) {
if (!myCircularQueueIsEmpty(obj)){
}
else {
return -1;
}
}

/** Get the last item from the queue. */
int myCircularQueueRear(MyCircularQueue* obj) {
if (!myCircularQueueIsEmpty(obj)){
return obj->value[obj->tail];
}else{
return -1;
}
}

/** Checks whether the circular queue is empty or not. */
bool myCircularQueueIsEmpty(MyCircularQueue* obj) {
if (obj == NULL){
return false;
}
if (obj->cnt == 0){
return true;
}
else{
return false;
}
}

/** Checks whether the circular queue is full or not. */
bool myCircularQueueIsFull(MyCircularQueue* obj) {
if (obj->cnt ==  obj->size ){
return true;
}
else{
return false;
}
}

void myCircularQueueFree(MyCircularQueue* obj) {

free(obj->value);
free(obj);
}

/**
* Your MyCircularQueue struct will be instantiated and called as such:
* MyCircularQueue* obj = myCircularQueueCreate(k);
* bool param_1 = myCircularQueueEnQueue(obj, value);

* bool param_2 = myCircularQueueDeQueue(obj);

* int param_3 = myCircularQueueFront(obj);

* int param_4 = myCircularQueueRear(obj);

* bool param_5 = myCircularQueueIsEmpty(obj);

* bool param_6 = myCircularQueueIsFull(obj);

* myCircularQueueFree(obj);
*/

Runtime: 24 ms
Memory Usage: 13.9 MB
``````