算法（4）—— 队列的链表实现

1. 队列的链表实现EnQueue 在尾节点，DeQueue 在首节点。

  1 #include  "fatal.h"
  2
  3 typedef int ElementType ;
  4 typedef struct QueueNode * Queue;
  5 typedef struct QueueNode * Position;
  6
  7 #define MAXSIZE (6)
  8
  9
 10 struct QueueNode  {
 11   ElementType data;
 12   Position Next;
 13   Position Rear;
 14   Position Front;
 15   int size;
 16 };
 17
 18 void DeleteQueue  (Queue Q);
 19 Queue MakeEmpty(Queue Q);
 20 int  IsEmpty  (Queue Q);
 21 int  IsFull (Queue Q);
 22 void EnQueue  (ElementType X, Queue Q);
 23 void DeQueue  (Queue Q);
 24 ElementType FrontAndDequeue (Queue);
 25
 26
 27
 28 int main(int argc, char *argv[])  {
 29   Queue Q;
 30   Q = MakeEmpty (NULL);
 31
 32   EnQueue (1,Q);
 33   EnQueue (2,Q);
 34
 35   ElementType X = 12 ;
 36
 37   while ( !IsEmpty(Q))  {
 38     printf ("%d ", Q->Front->data);
 39     DeQueue (Q);
 40   }
 41   printf("\n");
 42   printf("Empty = %c\n",IsEmpty(Q)?‘Y‘:‘N‘ );
 43
 44   Q = MakeEmpty (NULL);
 45   EnQueue (X,Q);
 46   EnQueue (21,Q);
 47   EnQueue (X,Q);
 48   printf("Queue is: ");
 49
 50   Position P = Q -> Front;
 51   while (P)  {
 52     printf ("%d ",P->data);
 53     P = P->Next;
 54   }
 55   printf("\n");
 56
 57   printf ("Front and Rear:%d %d  ",Q->Front->data,Q->Rear->data);
 58   printf("\n");
 59
 60   ElementType Y = FrontAndDequeue (Q);
 61   printf ("Del and Front:%d %d ", Y,Q->Front->data);
 62
 63   printf("\n");
 64   Y = FrontAndDequeue (Q);
 65   printf ("Del and Front:%d %d ", Y,Q->Front->data);
 66   printf("\n");
 67
 68   Y = FrontAndDequeue (Q);
 69   printf ("Del and Front:%d %d\n", Y,(Q->Front == Q?0:Q->Front->data));
 70
 71   DeQueue (Q);    //do not Del any node
 72   DeQueue (Q);
 73
 74   printf("size = %d\n",Q->size);
 75
 76   return 0;
 77
 78 }
 79
 80
 81 void Delete (Queue Q)  {
 82   if ( Q = NULL)
 83     Error ("Out of space.");
 84   Position P, tmp;
 85   P = Q->Next;
 86   Q -> Next = NULL;
 87
 88   while ( P != NULL)  {
 89     tmp = P -> Next;
 90     free (P);
 91     P = tmp;
 92   }
 93 }
 94
 95 Queue MakeEmpty (Queue Q)  {
 96   if ( Q != NULL)
 97     Delete (Q);
 98
 99   Q = malloc (sizeof (struct QueueNode));
100   if ( Q == NULL)  Error ("Out of memory.");
101   Q -> Next = NULL;
102   Q -> Rear = Q;
103   Q -> Front = Q->Next;
104   Q-> size = 0;
105   return Q;
106 }
107
108 int IsFull (Queue Q)  {
109   return Q->size == MAXSIZE;
110 }
111
112 int IsEmpty (Queue Q)  {
113   return Q->size == 0;
114 }
115
116 void EnQueue  (ElementType X, Queue Q)  {
117   if ( Q == NULL ) Error ("Out of space.");
118
119   Position tmp;
120   tmp = malloc (sizeof (struct QueueNode));
121   if (tmp == NULL)  Error ("Out of space,");
122
123   tmp -> data = X;
124   Q -> Rear -> Next = tmp;
125   Q -> Rear = tmp;
126   Q -> Rear -> Next = NULL;
127   Q -> Front = Q -> Next;
128   Q->size++;
129
130   if (Q -> size > MAXSIZE)  Error ("Too large.");
131
132 }
133
134 void DeQueue  (Queue Q)  {
135   if (IsEmpty(Q))  Error ("Empty Queue.");
136
137   Position tmp = Q -> Front;
138   Q -> Next = tmp -> Next;
139    free(tmp);
140   if (Q -> Front == Q->Rear)  { Q->Front = Q;}
141   else {   Q -> Front = Q->Next;  }
142   Q->size--;
143 }
144
145 ElementType FrontAndDequeue ( Queue Q)  {
146   ElementType X;
147   if (IsEmpty (Q))  Error ("Empty Queue.");
148
149   X = Q ->Front->data;
150   Position t = Q->Front;
151   Q -> Next = t-> Next;
152   if (Q -> Front == Q->Rear)  { Q->Front = Q;}
153   else {   Q -> Front = Q->Next;  }
154   free (t);
155   Q -> size--;
156
157   return X;
158 }