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Linked lists

Basic ideas about linked list

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Linked lists

  1. 1. Linked Lists
  2. 2. 2 Anatomy of a linked list  A linked list consists of:  A sequence of nodes a b c d  Each node contains a value  and a link (pointer or reference) to some other node  The last node contains a null link  The list may (or may not) have a header myList  myList isn’t a header, it’s just a reference
  3. 3. 3 More terminology  A node’s successor is the next node in the sequence  The last node has no successor  A node’s predecessor is the previous node in the sequence  The first node has no predecessor  A list’s length is the number of elements in it  A list may be empty (contain no elements)
  4. 4. 4 Creating links typedef struct link { int data; struct link *next; }myList; myList *head, *tail; int main() { myList *p, *q; p=(myList*)malloc(sizeof(myList)); q=(myList*)malloc(sizeof(myList)); p->data=44; q->data=97; p->next=q; q->next=0;  } data next pointer data next data next p: q: 44 97 next next p: q: 44 97 p: q:
  5. 5. 5 Singly-linked lists  Here is a singly-linked list (SLL):  Each node contains a value and a link to its successor (the last node has no successor)  We have a reference to the first node in the list  The reference is null if the list is empty a b c d myList
  6. 6. 6 Creating a simple list  A head node is just an initial node that exists at the front of every list, even when the list is empty  The purpose is to keep the list from being null, and to point at the first element  A tail node is just an initial node that exists at the end of every list, even when the list is empty.  The purpose is to keep the list from being null, and to point at the last element  In the previous code, just add this in main: head=p tail=q 44 97 p: q: head: tail:
  7. 7. 7 Traversing a SLL  The following method traverses a list (and prints its elements): void traverse() { p=head; while(p!=0) { printf(“%d “, p->data); p=p->next; }
  8. 8. 8 Traversing a SLL (animation) 489744 head p
  9. 9. 9 Inserting a node into a SLL  There are many ways you might want to insert a new node into a list:  As the new first element  As the new last element  Before a given value  After a given value  All are possible, but differ in difficulty
  10. 10. 10 Inserting as a new last element  This is probably the easiest method to implement  void insertAtLast(int value) { p=(myList*)malloc(sizeof(myList)); p->data=value; p->next=tail->next; tail=p; }  Use this as: insertAtLast(value);
  11. 11. 11 Inserting at last (animation) 9744 head 48p Find the tail node First, copy the link from the node that’s already in the list Then, change the link in the node that’s already in the list tail Then, change the link in the tail node Example: Call: insertAtLast(48)
  12. 12. 12 Inserting a node as a new first element  void insertAtFirst(int value) { p=(myList*)malloc(sizeof(myList)); p->data=value; p->next=head; head=p; }  Use this as: insertAtFirst(value)
  13. 13. 13 Inserting at first (animation) 9744 head 14p Find the head node First, change the link in the new node tail Then, change the link in the head node 48 Example: Call: insertAtFirst(14)
  14. 14. 14 Inserting a node as a new first element  void insertAtMiddle(int search_data, int value) { q=head; while(q!=0) { if(q->data==search_data) { p=(myList*)malloc(sizeof(myList)); p->data=value; p->next=q->next; q->next=p; } p=p->next; } Use this as: insertAtMiddle(search_data, value) Don’t change the sequence
  15. 15. 15 Inserting after (animation) 489744 head 29p Find the node you want to insert after First, copy the link from the node that’s already in the list Then, change the link in the node that’s already in the list q Example: Call: insertAtMiddle(29)
  16. 16. 16 Deleting a node from a SLL  In order to delete a node from a SLL, you have to change the link in its predecessor  This is slightly tricky, because you can’t follow a pointer backwards  Deleting the first node in a list is a special case, because the node’s predecessor is the list header
  17. 17. 17 Inserting as a new last element  This is probably the easiest method to implement  void delete(int value) { q=0; p=head; while(p!=0) { if(p->data==value) { if(p==head) head=p->next; else q->next=p->next; } q=p; p=p->next; } Use this as: delete(value);
  18. 18. 18 Deleting an element from a SLL 489744 head • To delete the first element, change the link in the header • To delete some other element, change the link in its predecessor • What will happen for last node??? Code &Visualize yourself (predecessor) 974414 head 48 q p p
  19. 19. 19 Other operations on linked lists  Most “algorithms” on linked lists—such as insertion, deletion, and searching—are pretty obvious; you just need to be careful  Sorting a linked list is just messy, since you can’t directly access the nth element—you have to count your way through a lot of other elements Question: How would you reverse a singly-linked list in place (that is, without creating any new nodes)?
  20. 20. 20 The End

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  • ssuserdc1fe1

    May. 12, 2017
  • MonaSweetie

    Jan. 23, 2021

Basic ideas about linked list

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