《刊首寄语Titl》PPT课件.ppt

Queue C and Data Structures Baojian Hua Linear List nRecall that a linear list has the form: nThe delete and insert operations may insert or delete an arbitrary element e_i nIf the delete is restricted at one end and insert at the other end, we get a queue Example: Queue of Char a insert b a insert insert b a c delete b c Abstract Data Types in C: Interface / in file “queue.h” #ifndef QUEUE_H #define QUEUE_H typedef struct Queue_t *Queue_t; Queue_t Queue_new (); int Queue_size (Queue_t q); int Queue_isEmpty (Queue_t q); void Queue_enQueue (Queue_t q, poly x); poly Queue_deQueue (Queue_t q); poly Queue_getHead (Queue_t q); #endif Implementation Using Extensible Array / in file “arrayQueue.c” #include “queue.h” struct Queue_t Array_t l; ; / Recall the box strategy: l q Operations: “new” Queue_t Queue_new () Queue_t q = malloc (sizeof (*q); q-l = Array_new (); return q; 0 n-1 array max tail l q Operations: “size” int Queue_size (Queue_t q) return Array_length (q-l); 0 n-1 array max tail l q Operations: “isEmpty” int Queue_isEmpty (Queue_t q) return Array_isEmpty (q-l); 0 n-1 array max tail l q Operations: “enQueue” void Queue_enQueue (Queue_t q, poly x) Array_insertLast (stk-l, x); return; 0 n-1 array max tail l q Operations: “deQueue” poly Queue_deQueue (Queue_t q) if (Array_isEmpty (q-l) error (“empty queue”); return Array_deleteFirst (q-l); Operations: “deQueue” 0 n-1 array max tail l q Operations: “deQueue” 0 n-1 array max tail l q Analysis nWhats the complexity? nenQueue: O(1) ndeQueue: O(n) ndata movement nCan we do better? nLazy approach nbetter amortized performance nCircular queue Lazy Approach nInstead of moving data when “deQueue”, we move data only when “enQueue” reaching the tail of the queue nO(n) on n operations nwhich has O(1) amortized cost Lazy Approach nWhats necessary modification? nLeave this as a programming assignment 0 n-1 array max tail l q Circular Queue nA refinement of the lazy approach is the circular queue head = tail = 0; 0 1 2 3 4 5 tail head enQueue (q, a); Circular Queue nA refinement of the lazy approach is the circular queue head = tail = 0; 0 1 2 3 4 5 tail head enQueue (q, a); enQueue (q, b); a Circular Queue nA refinement of the lazy approach is the circular queue head = tail = 0; 0 1 2 3 4 5 tail head enQueue (q, a); enQueue (q, b); enQueue (q, c); a b Circular Queue nA refinement of the lazy approach is the circular queue head = tail = 0; 0 1 2 3 4 5 tail head enQueue (q, a); enQueue (q, b); enQueue (q, c); enQueue (q, d); a b c Circular Queue nA refinement of the lazy approach is the circular queue head = tail = 0; 0 1 2 3 4 5 tail head enQueue (q, a); enQueue (q, b); enQueue (q, c); enQueue (q, d); enQueue (q, e); a b c d Circular Queue nA refinement of the lazy approach is the circular queue head = tail = 0; 0 1 2 3 4 5tail head enQueue (q, a); enQueue (q, b); enQueue (q, c); enQueue (q, d); enQueue (q, e); a b c d e enQueue (q, f); ? Circular Queue nA refinement of the lazy approach is the circular queue Empty: head = tail; Full: tail+1 = head ? General Equations: head = (head+1)%N; tail = (tail+1)%N; 0 1 2 3 4 5tail head a b c d e Circular Queue / Cook these together, we can implement the / input buffer using queue: struct Buffer_t char buf128; int head; int tail; ; struct Buffer_t Buffer_t; / Rethink the key pressing, and “getchar ()”? Implementation Using Linked List / in file “linkedQueue.c” #include “queue.h” struct Queue_t List_t l; ; l q data next data next data next Operations: “new” Queue_t Queue_new () Queue q = malloc (sizeof (*q); q-l = LinkedList_new (); return q; l q / / Operations: “size” int Queue_size (Queue_t q) return LinkedList_length (q-l); l q data next data next data next Operations: “isEmpty” int Queue_isEmpty (Queue_t q) return LinkedList_isEmpty (q-l); l q data next data next data next Operations: “enQueue” void Queue_enQueue (Queue_t q, poly x) / note the difference with extensible array- / based representation LinkedList_insertLast (q-l, x); return; l q data next data next data next Operations: “deQueue” poly Queue_deQueue (Queue_t q) if (LinkedList_isEmpty (q-l) error (“empty queue”); return LinkedList_deleteFirst (q-l); l q data next data next data next Analysis nWhats the complexity of these operations? nenQueue: O(n) nsearch the last element ndeQueue: O(1) nImprovement: Circular linked 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