队列的链表实现

/*
  队列的链表实现。
  队列是一种在表头删除，表尾插入的表。
  队列的出队和入队操作要更新队尾和队头。
  对于带头结点的队列，当队尾指向头结点，队头指向NULL则队列为空对。 
*/

/*接口头文件*/
typedef int ElementType;
#ifndef _QUEUE_H
#define _QUEUE_H
#include <stdbool.h>

struct Node;
typedef struct Node * PtrToNode;
typedef PtrToNode Queue;
typedef PtrToNode Position;

/*操作集*/
Queue CreateQueue( void );
void MakeEmpty( Queue Q );
bool IsEmpty( Queue Q );
void Enqueue( ElementType X, Queue Q );
void Dequeue( Queue Q );
ElementType Front( Queue Q );
ElementType FrontAndDequeue( Queue Q );
void DisposeQueue( Queue Q );
void PrintfQueue( Queue Q );

#endif 


/*接口实现*/
#include <stdio.h>
#include <stdlib.h>
#include "queue.h"

/*特定结构体定义*/
struct Node
{
    ElementType Element;
    Position Next;
    Position Front;   //队头 
    Position Rear;    //队尾 
};

/*创建队列*/
Queue CreateQueue( void )
{
    Queue Q;
    
    Q = ( Queue )malloc( sizeof( struct Node ) );
    if ( Q == NULL )
    {
       printf( "No Space!!!
" );
       exit( 1 );
    }
    Q->Next = NULL;
    /*初始化为空队*/
    MakeEmpty( Q );
    
    return Q; 
}

/*使队列为空*/
void MakeEmpty( Queue Q )
{
    if ( ! IsEmpty( Q ) )
       DisposeQueue;
    
    Q->Front = NULL;
    Q->Rear = Q;
    Q->Element = 0;
}

bool IsEmpty( Queue Q )
{
    return Q->Next == NULL;
}

void DisposeQueue( Queue Q )
{
    Position Temp;
    Position P;
    
    P = Q->Next;
    Q->Next = NULL;
    
    while ( P != NULL )
    {
        Temp = P->Next;
        free( P );
        P = Temp;
    }
}

void Enqueue( ElementType X, Queue Q )
{
    Position NewNode;
    
    NewNode = ( Queue )malloc( sizeof( struct Node ) );
    if ( NewNode == NULL )
    {
       printf( "No Space!!!
" );
       exit( 1 );
    }
    else
    {
        NewNode->Element = X;
        NewNode->Next = NULL;
        
        if ( IsEmpty( Q ) )
           Q->Front = NewNode;
           
        Q->Rear->Next = NewNode;
        
        Q->Rear = NewNode;
        Q->Element++;
    }
}

void Dequeue( Queue Q )
{
    if ( IsEmpty( Q ) )
    {
       printf( "Queue is empty
" );
       exit( 1 );
    }
    else
    {
        if ( Q->Next->Next == NULL )
           Q->Rear = Q;
           
        Q->Front = Q->Front->Next;
        free( Q->Next );
        Q->Next = Q->Front;
        Q->Element--;
    }
}

ElementType Front( Queue Q )
{
    if ( IsEmpty( Q ) )
    {
       printf( "Queue is empty
" );
       exit( 1 );
    }
    else
        return Q->Front->Element;
}

ElementType FrontAndDequeue( Queue Q )
{
    ElementType n;
    
    if ( IsEmpty( Q ) )
    {
       printf( "Queue is empty
" );
       exit( 1 );
    }
    else
    {
        n = Q->Front->Element;
        if ( Q->Next->Next == NULL )
           Q->Rear = Q;
           
        Q->Front = Q->Front->Next;
        free( Q->Next );
        Q->Next = Q->Front;
        Q->Element--;
        return n;
    }
}

void PrintfQueue( Queue Q )
{
    while ( ! IsEmpty( Q ) )
        printf( "%3d",FrontAndDequeue( Q ) );
    
    printf( "
" );
}