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Linked Lists
COMP
Fall 2006
List Overview
Linked lists
Abstract data type (ADT)
Basic operations of linked lists
Insert, find, delete, print, etc.
Variations of linked lists
Circular linked lists
Doubly linked lists
A Simple Linked List Class
We use two classes: Node and List
Declare Node class for the nodes
data: double-type data in this example
next: a pointer to the next node in the list
class Node {
public:
double data; // data
Node* next; // pointer to next
A Simple Linked List Class
Declare List, which contains
head: a pointer to the first node in the list.
Since the list is empty initially, head is set to NULL
Operations on List
class List {
public:
List(void) { head = NULL; } // constructor
~List(void); // destructor
bool IsEmpty() { return head == NULL; }
Node* InsertNode(int index, double x);
int FindNode(double x);
int DeleteNode(double x);
void DisplayList(void);
private:
Node* head;
Inserting a new node
Node* InsertNode(int index, double x)
Insert a node with data equal to x after the index’th elements.
(i.e., when index = 0, insert the node as the first element; when index = 1, insert the node after the first element, and so on)
If the insertion is successful, return the inserted node.
Otherwise, return NULL.
(If index is < 0 or > length of the list, the insertion will fail.)
Steps
1. Locate index’th element
2. Allocate memory for the new node
3. Point the new node to its successor
4. Point the new node’s predecessor to the new node
newNode
index’th element
Inserting a new node
Possible cases of InsertNode
1. Insert into an empty list
2. Insert in front
3. Insert at back
4. Insert in middle
But, in fact, only need to handle two cases
Insert as the first node (Case 1 and Case 2)
Insert in the middle or at the end of the list (Case 3 and
Case 4)
Inserting a new node
Node* List::InsertNode(int index, double x) { if (index < 0) return NULL;
int currIndex = 1; Node* currNode = head; while (currNode && index > currIndex) { currNode = currNode->next; currIndex++; } if (index > 0 && currNode == NULL) return NULL;
Node* newNode = new Node; newNode->data = x; if (index == 0) { newNode->next = head; head = newNode; } else { newNode->next = currNode->next; currNode->next = newNode; } return newNode; }
Create a new node
Inserting a new node
Node* List::InsertNode(int index, double x) { if (index < 0) return NULL;
int currIndex = 1; Node* currNode = head; while (currNode && index > currIndex) { currNode = currNode->next; currIndex++; } if (index > 0 && currNode == NULL) return NULL;
Node* newNode = new Node; newNode->data = x; if (index == 0) { newNode->next = head; head = newNode; } else { newNode->next = currNode->next; currNode->next = newNode; } return newNode; }
Insert as first element
head
newNode
Finding a node
int FindNode(double x)
Search for a node with the value equal to x in the list.
If such a node is found, return its position. Otherwise, return
int List::FindNode(double x) {
Node* currNode = head;
int currIndex = 1;
while (currNode && currNode->data != x) {
currNode = currNode->next;
currIndex++;
if (currNode) return currIndex;
return 0;
Deleting a node
int DeleteNode(double x)
Delete a node with the value equal to x from the list.
If such a node is found, return its position. Otherwise, return
Steps
Find the desirable node (similar to FindNode)
Release the memory occupied by the found node
Set the pointer of the predecessor of the found node to the
successor of the found node
Like InsertNode, there are two special cases
Delete first node
Delete the node in middle or at the end of the list
Deleting a node
int List::DeleteNode(double x) { Node* prevNode = NULL; Node* currNode = head; int currIndex = 1; while (currNode && currNode->data != x) { prevNode = currNode; currNode = currNode->next; currIndex++; } if (currNode) { if (prevNode) { prevNode->next = currNode->next; delete currNode; } else { head = currNode->next; delete currNode; } return currIndex; } return 0; }
prevNode currNode
Deleting a node
int List::DeleteNode(double x) { Node* prevNode = NULL; Node* currNode = head; int currIndex = 1; while (currNode && currNode->data != x) { prevNode = currNode; currNode = currNode->next; currIndex++; } if (currNode) { if (prevNode) { prevNode->next = currNode->next; delete currNode; } else { head = currNode->next; delete currNode; } return currIndex; } return 0; }
head currNode
Destroying the list
~List(void)
Use the destructor to release all the memory used by the list.
Step through the list and delete each node one by one.
List::~List(void) {
Node* currNode = head, *nextNode = NULL;
while (currNode != NULL)
nextNode = currNode->next;
// destroy the current node
delete currNode;
currNode = nextNode;
Using List
int main(void)
List list;
list.InsertNode(0, 7.0); // successful
list.InsertNode(1, 5.0); // successful
list.InsertNode(-1, 5.0); // unsuccessful
list.InsertNode(0, 6.0); // successful
list.InsertNode(8, 4.0); // unsuccessful
// print all the elements
list.DisplayList();
if(list.FindNode(5.0) > 0) cout << "5.0 found" << endl;
else cout << "5.0 not found" << endl;
if(list.FindNode(4.5) > 0) cout << "4.5 found" << endl;
else cout << "4.5 not found" << endl;
list.DeleteNode(7.0);
list.DisplayList();
return 0;
6 7 5 Number of nodes in the list: 3 5.0 found 4.5 not found 6 5 Number of nodes in the list: 2
result