418115: การเขียนโปรแกรมโครงสร้าง โครงสร้างข้อมูล II

418115: การเขียนโปรแกรมโครงสร้างโครงสร้างข้อมูล II ประมุข ขันเงิน

Linked List • A linked list can be thought of a chain of linked list elements. • A linked list element contains a single data item, and contains a pointer to the next linked list element. • It may also contain a pointer to the previous linked list element. In this case, we call it a doubly linked list element.

Linked List (cont.) 11 42 7 128 398 4649

Linked List Implementation struct_LLElement { intdata; _LLElement*next,*prev; }; typedefstruct_LLElementLLElement;

Linked List Implementaion (cont.) • LLElement*LLElement_new(intdata) • used to create a new linked list element with the given data. • Usage: LLElement*element=LLElement_new(10);

Linked List Implementation (cont.) LLElement*LLElement_new(intdata) { LLElement*result= (LLElement*)malloc(sizeof(LLElement)); if(result!=NULL) { result->data=data; result->next=NULL; result->prev=NULL; } returnresult; }

Linked List Implementaion (cont.) • voidLLElement_insert_after( LLElement*position,LLElement*e) • inserts a linked list element “e” after “position”.

Linked List Implementation (cont.) 11 42 7 128 398 4649 e 192 this

Linked List Implementation (cont.) voidLLElement_insert_after( LLElement*position,LLElement*e) { e->prev=position; e->next=position->next; if(position->next!=NULL) position->next->prev=e; position->next=e; }

Linked List Implementaion (cont.) • voidLLElement_insert_before(LLElement*position,LLElement*e) • inserts the linked list element “e” before “position”.

Linked List Implementation (cont.) 11 42 7 position 128 398 4649 e 192

Linked List Implementation (cont.) 11 42 7 this 128 398 4649 e 192

Linked List Implementation (cont.) voidLLElement_insert_before( LLElement*position,LLElement*e) { e->next=position; e->prev=position->prev; if(prev!=NULL) position->prev->next=e; position->prev=e; }

Linked List Implementaion (cont.) • voidLLElement_remove(LLElement*e) • removes the linked list element “e” from the chain. • In effect, it links e’s prev with next.

Linked List Implementation (cont.) 11 42 7 128 398 4649 this

Linked List Implementation (cont.) 11 42 7 128 398 4649 e

Linked List Implementation (cont.) voidLLElement_remove(LLElement*e) { if(e->prev!=NULL) e->prev->next=e->next; if(e->next!=NULL) e->next->prev=e->prev; e->prev=NULL; e->next=NULL; }

Linked List Element’s Efficiency? • Space: O(1) • Running Time • InsertBefore O(1) • InsertAfter O(1) • Remove O(1)

Implementing List with Linked List • To simplify implementation, we will use two “dummy” elements to act as the first element and the last element of the list. • These two dummies do not hold real data. • Elements between them do.

Implementing List with Linked List(cont.) head ??? 11 42 7 128 398 4649 tail ???

Implementing List with Linked List (cont.) typedefstruct{ LLElement*head,*tail; intsize; }LinkedList; • size คือจำนวนสมาชิกใน linked list

Implementing List with Linked List (cont.) • voidLinkedList_init(LinkedList*list) • Initializes a linked list. • Create the head element. • Create the tail element. • Link them together. • Set the size to 0. voidLinkedList_init(LinkedList*list) { list->head=LLElement_new(0); list->tail=LLElement_new(0); list->head->next=tail; list->tail->prev=head; list->size=0; } tail head 0 0

Implementing List with Linked List (cont.) intLinkedList_get(LinkedList*list,inti) { intj; LLElement*ptr=list->head->next; for(j=0;j<i;j++) ptr=ptr->next; returnptr->data; }

Implementing List with Linked List (cont.) voidLinkedList_set(LinkedList*list,inti,intx) { intj; LLElement*ptr=list->head->next; for(j=0;j<i;j++) ptr=ptr->next; ptr->data=x; }

Implementing List with Linked List (cont.) voidLinkedList_find(LinkedList*list,intx) { intresult=0; LLElement*ptr=list->head->next; while(ptr!=list->tail&&ptr->data!=x) { ptr=ptr->next; result++; } if(ptr==tail) return-1; else returnresult; }

Implementing List with Linked List (cont.) voidLinkedList_insert(LinkedList*list,inti,intx) { LLElement*ptr=list->head; intj; for(j=0;j<i-1;j++) ptr=ptr->next; LLElement_insert_after(ptr,LLElement_new(x)); list->size++; }

Implementing List with Linked List (cont.) voidLinkedList_remove(LinkedList*list,inti) { LLElement*ptr=head->next; intj; for(j=0;j<i;j++) ptr=ptr->next; LLElement_remove(ptr); free(ptr); list->size--; }

Linked List Implementation’s Efficiency • Space: O(n) • Running Time: • Get(i) O(i) = O(n) • Set(x,i) O(i) = O(n) • Find(x) O(n) • Insert(x,i) O(i) = O(n) • Remove(x,i) O(i) = O(n)

Linked List Implementation’s Efficiency (cont.) • Notice that how you specify the operations can have a lot of impact on the implementation’s efficiency. • We can insert a linked list element into a linked list in O(1) if you know the element just before or after it. • But, if we are given the position i to insert, it takes O(i) time just to get there.

Linked List Implementation’s Efficiency (cont.) • How is linked list better than array? • The space is O(n) at all time. • More efficient use of memory. • It performs some operation faster. • Insert(x, 0) • Remove(0) • Both are O(1) in LinkedList, but O(n) in ArrayList. • So, a queue implemented by a linked list takes O(1) per operation.

418115: การเขียนโปรแกรมโครงสร้าง โครงสร้างข้อมูล II

418115: การเขียนโปรแกรมโครงสร้าง โครงสร้างข้อมูล II

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418115: การเขียนโปรแกรมโครงสร้าง โครงสร้างข้อมูล II