朝陽科技大學資管系 李麗華 第四章 鏈結串列 Linked List Fools look to tomorrow, wise men use tonight.

李麗華 -- 資料結構講義 練功前的沉思 Q1: Remember the pointer in C? Q2: What is linked list? Q3: What is single linked list? Q4: What is circular linked list? Q4: How to implement linked list using C? Q5: What is the difference between linked list and array? ( 優缺點 ) Q6: When do I apply linked list to solve problems? Q7: Do you aware any problem for link list?

李麗華 -- 資料結構講義 Review of Pointer in C The pointer data type in C means the data stores the address that this address points to other data with the same type). EX: int i, *ptr, *p ; i=10 ; ptr = &i ; p= (int *) malloc(sizeof(int)) ; *p = 1024 ; printr(“i=%d, *ptr=%d, *p=%d ”, i, *ptr, *p) free(p); 將記憶體釋回 10 i FFF0 ptr FFF2 address ? p FFF A 取得記憶體

李麗華 -- 資料結構講義 What is linked list? Def: A link list is a dynamic allocating list in which data is stored in a node and pointer(s) is used to indicate the position of the list. Characteristics: 1. The list is a dynamically allocated structure. 2. The size of the storage do not need to be declared in advance. 3.Dynamically create/dispose the node when a node is inserted/deleted. 4.Insertion and deletion can be done without any order. node data ptr

李麗華 -- 資料結構講義 The data structure of a node Example of a node declared in C: struct node { int data; <-- 資料型態可自訂 struct node *next; } Initialize a linked list, i.e., head = tail = NULL; head -> link = NULL; tail -> link = NULL head next NULL 若指標指向 NULL, 有時亦可畫成 : data next 放資料內容 放指標 Create a node: x=(struct node *)malloc(sizeof(struct node)); 名稱自訂, 例如可叫 head,tail,ptr,x,y,z, …

李麗華 -- 資料結構講義 Single Linked List A single linked list is a dynamic allocated list where nodes are linked by one way pointer. Insertion and deletion of a node can be done in any position of a list. Head DOGCATBIRDBATAPE Tail

李麗華 -- 資料結構講義 Insert a node to the sorted list (1) 1. Get the memory for the new node x=(struct node *)malloc(sizeof(struct node)); x = num; ( 設 x 內存放某一數值 num) x->next = NULL ; 2. To insert a node in a sorted list, we search the list from “ head ” and find the right position. Three possible positions are considered. (1) insert to the head (2) insert to the middle (3) insert to the tail Insert to the head x->next = head ; head = x; Head Tail 10 x

李麗華 -- 資料結構講義 Insert a node to the sorted list (2) Insert to the tail tail->next = x ; tail = x; Head Tail 500 x Insert to the middle cur = head; while(x->data > cur->data) { pre = cur ; cur = cur -> next; } x->next = cur; pre -> next = x; Head Tail 250 x cur pre

李麗華 -- 資料結構講義 Delete a node from the sorted list (1) 1. Find the node in the list. Deletion should be taken care in three different positions. (1) Delete from head (2) Delete from middle (3) Delete from tail 2. When found the node, adjust the link and dispose the node. Dispose a node p: free(p) ; Delete from head: p = head ; head = head->next; free(p); Delete from tail: p = head ; while(p->next != tail) p = p ->next; p ->next = NULL; free(tail) ; tail = p;

李麗華 -- 資料結構講義 Delete a node from the sorted list (2) Delete a node in the middle cur = head; while(cur->next != NULL) { pre = cur ; cur = cur -> next; if (x->data == cur->data) { pre->next = cur->next; free(cur); } 令欲刪除 x->data=300 Head Tail 400 precur

李麗華 -- 資料結構講義 Join Two Lists Join x & y list into Z: struct node *c; if (x==NULL) z = y ; 當 x 的 list 為空 else if (y==NULL) z = x ; 當 y 的 list 為空 else { z = x ; c = x ; while(c->next!=NULL) c = c -> next; c -> next = y; } x y z

李麗華 -- 資料結構講義 Invert a List Invert a list: struct node *cur,*pre,*nex; nex = head; cur = NULL; while(nex != NULL) { pre = cur; cur = nex; nex = nex -> next cur-> next = pre; } tail = head; head = cur; HeadTail nex HeadTail HeadTail HeadTail pre HeadTail cur nex pre cur nex

李麗華 -- 資料結構講義 Circular List Def: A circular list is a list with its tail points to the head. Head Tail Insert node x to head When list is empty head=x; tail=x; x->next = x; Insert node x to head When list is not empty x->next = head; tail -> next = x; head=x; head x tail head x tail head

李麗華 -- 資料結構講義 Circular List Operation Insert node x to tail tail -> next = x; x->next = head; tail = x; Delete node p from head p = head; head = head -> next; tail -> next = head; free(p); Delete node p from tail p = head; while(p->next != tail) p= p-> next; p -> next = head; free(tail); tail = p; Delete node p from middle 做法與一般串列相同 請參考前面內容

李麗華 -- 資料結構講義 Join Two Circular Lists Join A & B circular list Atail -> next = Bhead; Btail -> next = Ahead; Ahead Atail Bhead BtailAhead Atail Bhead Btail

李麗華 -- 資料結構講義 Double Linked List The problem of single linked list is that the search can only be done through one way pointer. The double linked list is a type of circular list in which each node contains two way pointers. pre data next 放左指標 放資料 放右指標 Head Tail 10 struct node { int data ; <-- 資料型態可自訂 struct node *pre ; struct node *next ; }

李麗華 -- 資料結構講義 Double Linked List Operation(1) Insert node x to head When double linked list is empty head=x; tail=x; x->next = x; Insert node x to head When double linked list is not empty x->next = head; tail -> next = x; head=x; head x tail head x tail head

李麗華 -- 資料結構講義 Double Linked List Operation(2) Insert node x to tail tail -> next = x; x->next = head; tail = x; Delete node p from head p = head; head = head -> next; tail -> next = head; free(p); Delete node p from tail p = head; while(p->next != tail) p= p-> next; p -> next = head; free(tail); tail = p; Delete node p from middle 做法與一般串列相同 請參考前面內容

李麗華 -- 資料結構講義 Application—Stack & Queue

李麗華 -- 資料結構講義 Polynomial Addition

李麗華 -- 資料結構講義 大師 — 該動動腦囉 !! 第 1 題, 第 3 題 請寫出 double linked list 及 circular linked list 的反轉串列 之演算法. 回家動動腦 上課來發表 你知道 Linked List 的問題嗎 ? -- 如果不小心沒有將 pointer 處理好, 會產生哪些問題 ?? -- 如果忘了 free(ptr), 又會有什麼問題 ?? -- 如果指標指錯了, 又可能產生哪些問題 ??

李麗華 -- 資料結構講義 Worry is like a rocking chair--it will give you something to do but it won’t get you anywhere. 煩惱好像讓你的腦袋有事做, 但卻無法幫助你解決事情