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Chapter 5 introduces the often- used data structure of linked lists. This presentation shows how to implement the most common operations on linked lists. Linked Lists in Action CHAPTER 5 Data Structures and Other Objects

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For this presentation, nodes in a linked list are objects, as shown here. data_field link_field 10 data_field link_field 15 data_field link_field 7 null class node { public: typedef double value_type;... private value_type data_field; node *link_field; }; Declarations for Linked Lists

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The data_field of each node is a type called value_type, defined by a typedef. data_field link_field 10 data_field link_field 15 data_field link_field 7 null class node { public: typedef int value_type;... private value_type data_field; node *link_field; }; Declarations for Linked Lists

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Each node also contains a link_field which is a pointer to another node. data_field link_field 10 data_field link_field 15 data_field link_field 7 null class node { public: typedef int value_type;... private value_type data_field; node *link_field; }; Declarations for Linked Lists

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A program can keep track of the front node by using a pointer variable such as head_ptr in this example. Notice that head_ptr is not a node -- it is a pointer to a node. head_ptr data_field link_field 10 data_field link_field 15 data_field link_field 7 null

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Declarations for Linked Lists A program can keep track of the front node by using a pointer variable such as head_ptr. Notice that head_ptr is not a node -- it is a pointer to a node. We represent the empty list by storing null in the head pointer. head_ptr null

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void list_head_insert(node*& head_ptr, const node::value_type& entry); Inserting a Node at the Front We want to add a new entry, 13, to the front of the linked list shown here. 10 15 7 null head_ptr entry 13

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Inserting a Node at the Front Create a new node, pointed to by a local variable insert_ptr. 10 15 7 null head_ptr entry 13 insert_ptr void list_head_insert(node*& head_ptr, const node::value_type& entry);

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Inserting a Node at the Front insert_ptr = new node; 10 15 7 null head_ptr entry 13 insert_ptr void list_head_insert(node*& head_ptr, const node::value_type& entry);

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Inserting a Node at the Front 10 15 7 null head_ptr entry 13 insert_ptr 13 insert_ptr = new node; Place the data in the new node's data_field. void list_head_insert(node*& head_ptr, const node::value_type& entry);

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Inserting a Node at the Front 10 15 7 null head_ptr entry 13 insert_ptr 13 insert_ptr = new node; Place the data in the new node's data_field. Connect the new node to the front of the list. void list_head_insert(node*& head_ptr, const node::value_type& entry);

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Inserting a Node at the Front 10 15 7 null head_ptr entry 13 insert_ptr 13 insert_ptr = new node(entry, head_ptr); The correct new node can be completely created in one step by calling an appropriate node constructor. void list_head_insert(node*& head_ptr, const node::value_type& entry);

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Inserting a Node at the Front 10 15 7 null head_ptr entry 13 insert_ptr 13 insert_ptr = new node(entry, head_ptr); Make the old head pointer point to the new node. void list_head_insert(node*& head_ptr, const node::value_type& entry);

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Inserting a Node at the Front 10 15 7 null head_ptr entry 13 insert_ptr 13 insert_ptr = new node(entry, head_ptr); head_ptr = insert_ptr; void list_head_insert(node*& head_ptr, const node::value_type& entry);

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Inserting a Node at the Front insert_ptr = new node(entry, head_ptr); head_ptr = insert_ptr; 10 15 7 null head_ptr 13 When the function returns, the linked list has a new node at the front. void list_head_insert(node*& head_ptr, const node::value_type& entry);

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void list_head_insert(node*& head_ptr, const node::value_type& entry) { node *insert_ptr; insert_ptr = new node(entry, head_ptr); head_ptr = insert_ptr; } Inserting a Node at the Front

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void list_head_insert(node*& head_ptr, const node::value_type& entry) { node *insert_ptr; insert_ptr = new node(entry, head_ptr); head_ptr = insert_ptr; } Does the function work correctly for the empty list ?

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head_ptr entry 13 null Inserting a Node at the Front Does the function work correctly for the empty list ? void list_head_insert(node*& head_ptr, const node::value_type& entry) { node *insert_ptr; insert_ptr = new node(entry, head_ptr); head_ptr = insert_ptr; }

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Inserting a Node at the Front head_ptr entry 13 null insert_ptr 13 void list_head_insert(node*& head_ptr, const node::value_type& entry) { node *insert_ptr; insert_ptr = new node(entry, head_ptr); head_ptr = insert_ptr; } null

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Inserting a Node at the Front head_ptr entry 13 insert_ptr 13 null void list_head_insert(node*& head_ptr, const node::value_type& entry) { node *insert_ptr; insert_ptr = new node(entry, head_ptr); head_ptr = insert_ptr; }

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Inserting a Node at the Front head_ptr 13 null void list_head_insert(node*& head_ptr, const node::value_type& entry) { node *insert_ptr; insert_ptr = new node(entry, head_ptr); head_ptr = insert_ptr; } When the function returns, the linked list has one node.

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Caution! Always make sure that your linked list functions work correctly with an empty list. EMPTY LIST

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Pseudocode for Inserting Nodes Nodes are often inserted at places other than the front of a linked list. There is a general pseudocode that you can follow for any insertion function...

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Pseudocode for Inserting Nodes Determine whether the new node will be the first node in the linked list. If so, then there is only one step: list_head_insert(head_ptr, entry);

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Pseudocode for Inserting Nodes Determine whether the new node will be the first node in the linked list. If so, then there is only one step: Determine whether the new node will be the first node in the linked list. If so, then there is only one step: The function we already wrote list_head_insert(head_ptr, entry);

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Pseudocode for Inserting Nodes Determine whether the new node will be the first node in the linked list. If so, then there is only one step: list_head_insert(head_ptr, entry); A pointer to the head of the list

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Pseudocode for Inserting Nodes Determine whether the new node will be the first node in the linked list. If so, then there is only one step: list_head_insert(head_ptr, entry); The data to put in the new node

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Pseudocode for Inserting Nodes Otherwise (if the new node will not be first): Start by setting a pointer named previous_ptr to point to the node which is just before the new node's position.

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Pseudocode for Inserting Nodes 15 10 7 null head_ptr Otherwise (if the new node will not be first): Start by setting a pointer named previous_ptr to point to the node which is just before the new node's position. In this example, the new node will be the second node previous_ptr

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Pseudocode for Inserting Nodes 15 10 7 null head_ptr Otherwise (if the new node will not be first): Start by setting a pointer named previous_ptr to point to the node which is just before the new node's position What is the name of this orange pointer ? Look at the pointer which is in the node *previous_ptr previous_ptr

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Pseudocode for Inserting Nodes 15 10 7 null head_ptr Otherwise (if the new node will not be first): Start by setting a pointer named previous_ptr to point to the node which is just before the new node's position This pointer is called previous_ptr->link_field (although this name may be private to the node) What is the name of this orange pointer ? previous_ptr

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Pseudocode for Inserting Nodes 15 10 7 null head_ptr Otherwise (if the new node will not be first): Start by setting a pointer named previous_ptr to point to the node which is just before the new node's position previous_ptr->link_field points to the head of a small linked list, with 10 and 7 previous_ptr

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Pseudocode for Inserting Nodes 15 10 7 null head_ptr Otherwise (if the new node will not be first): Start by setting a pointer named previous_ptr to point to the node which is just before the new node's position. The new node must be inserted at the front of this small linked list. 13 Write one C++ statement which will do the insertion. previous_ptr

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Pseudocode for Inserting Nodes 15 10 7 null head_ptr Otherwise (if the new node will not be first): Start by setting a pointer named previous_ptr to point to the node which is just before the new node's position. 13 What might cause this statement to fail to compile? previous_ptr list_head_insert(previous_ptr->link_field, entry);

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Pseudocode for Inserting Nodes 15 10 7 null head_ptr Otherwise (if the new node will not be first): Start by setting a pointer named previous_ptr to point to the node which is just before the new node's position. 13 Use a node member function to get the link field if needed. previous_ptr list_head_insert(previous_ptr->link( ), entry);

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Pseudocode for Inserting Nodes Determine whether the new node will be the first node in the linked list. If so, then there is only one step: list_head_insert(head_ptr, entry); Otherwise (if the new node will not be first): Set a pointer named previous_ptr to point to the node which is just before the new node's position. Make the function call: list_head_insert(previous_ptr->link( ), entry);

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Pseudocode for Inserting Nodes The process of adding a new node in the middle of a list can also be incorporated as a separate function. This function is called list_insert in the linked list toolkit of Section 5.2. The process of adding a new node in the middle of a list can also be incorporated as a separate function. This function is called list_insert in the linked list toolkit of Section 5.2.

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Pseudocode for Removing Nodes Nodes often need to be removed from a linked list. As with insertion, there is a technique for removing a node from the front of a list, and a technique for removing a node from elsewhere. Well look at the pseudocode for removing a node from the front of a linked list.

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Removing the Head Node 10 15 7 null head_ptr 13 Start by setting up a temporary pointer named remove_ptr to the head node. remove_ptr

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Removing the Head Node 10 15 7 null head_ptr 13 Set up remove_ptr. head_ptr = remove_ptr->link( ); remove_ptr Draw the change that this statement will make to the linked list.

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Removing the Head Node 10 15 7 null head_ptr 13 Set up remove_ptr. head_ptr = remove_ptr->link( ); remove_ptr

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Removing the Head Node Set up remove_ptr. head_ptr = remove_ptr->link( ); delete remove_ptr; // Return the node's memory to heap. 10 15 7 null head_ptr 13 remove_ptr

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Removing the Head Node Heres what the linked list looks like after the removal finishes. 10 15 7 null head_ptr

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It is easy to insert a node at the front of a list. The linked list toolkit also provides a function for inserting a new node elsewhere It is easy to remove a node at the front of a list. The linked list toolkit also provides a function for removing a node elsewhere--you should read about this function and the other functions of the toolkit. Summary

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T HE E ND Presentation copyright 2010, Addison Wesley Longman, For use with Data Structures and Other Objects Using C++ by Michael Main and Walter Savitch. Some artwork in the presentation is used with permission from Presentation Task Force (copyright New Vision Technologies Inc) and Corel Gallery Clipart Catalog (copyright Corel Corporation, 3G Graphics Inc, Archive Arts, Cartesia Software, Image Club Graphics Inc, One Mile Up Inc, TechPool Studios, Totem Graphics Inc). Students and instructors who use Data Structures and Other Objects Using C++ are welcome to use this presentation however they see fit, so long as this copyright notice remains intact.

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