This article is a linear structure (queue) of the data structure, and it is an integrated note based on the online course.
What is a queue
Queue : a linear table with certain operational constraints
Insert and delete operations: You can only insert at one end and delete at the other end.
- Data insertion: into the queue (AddQ)
- Data deletion: out of the queue (DeleteQ)
- First come first serve
- First in first out: FIFO
Description of the abstract data type of the queue
类型名称: Queue
数据对象集: A finite linear table with 0 or more elements.
操作集: Queue Q "Queue with a length of Maxsize, queue element item "ElementType
1.Queue CreatQueue(int MaxSize): Generate an empty queue with a length of MaxSize;
2.int IsFullQ(Queue q,int MaxSize): Determine whether the queue Q is full;
3.void AddQ (Queue Q, ElementType item): insert the data element item into the queue Q;
4.int IsEmptyQ(Queue Q): Determine whether the queue Q is empty;
5. ElementType DeleteQ (Queue Q): delete the head data element from the queue and return it.
Queue's sequential storage implementation
The sequential storage structure of the queue usually consists of a one-dimensional array and a variable front that records the position of the head element of the queue (pointing to the previous one of the head element of the queue, or -1 if there is no deletion) and a variable rear that records the position of the tail element of the queue . (When front===rear, the queue is empty)
#define MaxSize<储存数据元素的最大个数>
struct QNode{
ElementType Data[MaxSize];
int rear;
int front;
};
typedef struct QNode*Queue;
[Example] A work queue
Thinking:
(1) This scheme: What are the criteria for judging whether the stack is empty or full?
solution:
- Use additional tags: Size (number of elements, +1 when adding an element, -1 when deleting an element, empty or full according to Size of 0 or 1) or tag (tag is 1 when inserting an element, deleting one When the element tag is 0, the last operation is judged according to the tag being 0 or 1, so as to judge whether it is empty or full)
- Use only n-1 array spaces
(2) Why can't distinguish between empty and full? root cause?
Judging by the gap between front and rear, there are 6 situations in the above picture: 0,1,2,3,4,5
In the above figure, there are 7 types of loading elements in the queue: 0 (empty queue), 1 (one element), 2, 3, 4, 5, 6
Therefore, there are n types of gaps in the queue and n+1 types of the number of elements loaded in the queue, which must be contradictory.
(1) Into the queue
void AddQ(Queue PtrQ,ElementType item)
{
if((PtrQ->rear+1)%MaxSize == PtrQ->front){
printf("队列满")；
return;
}
PtrQ->rear = (PtrQ->rear+1)%MaxSize;
PtrQ->Data[PtrQ->rear]=item;
}
(2) Out of the queue
ElementType DeleteQ(Queue PtrQ)
{
if(PtrQ->front == PtrQ->rear){
printf("队列空")；
return ERROR;
}else{
PtrQ->front = (PtrQ->front+1)%MaxSize;
return PtrQ->Data[PtrQ->front];
}
}
The movement of the front and rear pointers adopts the " add 1 to take the remainder " method, which reflects the " recycling use " of sequential storage .
Chain storage implementation of queue
The chained storage structure of the queue can also be implemented with a singly linked list . Insert and delete operations are performed at the two ends of the linked list respectively
struct Node{
ElementType Data;
struct Node *Next;
};
struct QNode{
/*链队列结构*/
struct Node *rear; /*指向队尾结点*/
struct Node *front；/*指向队头结点*/
}；
typedef struct QNode*Queue;
Queue PtrQ;
Idea map:
- Chain without head node queue dequeue one example:
ElementType DeleteQ(Queue PtrQ)
{
struct Node *FrontCell;
ElementType FrontElem;
if(PtrQ->front==NULL){
printf("队列空")；
return ERROR;
}
FrontCell=Ptrq->front;
if(PtrQ->front==PtrQ->Rear)/*若队列只有一个元素*/
PtrQ->front = PtrQ->rear = NULL;/*删除后队列置为空*/
else
PtrQ->front = PtrQ->front->Next;
FrontElem = FrontCell->Data;
free(FrontCell);/*释放被删除结点空间*/
return FrontElem;
}
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If there are errors, confusions, etc. in the article, criticisms and corrections are welcome!