The implementation includes methods for adding, removing and iterating through the circular list. From these methods, the remove( Object ) method required more testing.
class Node {
Object data;
Node next;
public Node( Object data ) {
this.data = data;
}
public Node( Object data, Node next ) {
this.data = data;
this.next = next;
}
}
public class CircularLinkedList {
Node entryNode;
/**
* Adds a node to the circular linked-list via the entry node.
*/
public void add( Object data ) {
if( entryNode == null ) {
// Initialize the entry node.
//
entryNode = new Node( data ); // cant be null bec. self loop has to assigned.
// Link entry node to self, as there is only one node on the list.
entryNode.next = entryNode; // note apply it as it is circular.
/// Note- dont do this. we use this for forward traversal.
/// entryNode = entryNode.next;
} else {
// Add the node to the circular linked-list.
entryNode.next = new Node( data, entryNode.next );
}
}
/**
* Removes the first occurrence of the node (as specified by the data).
*/
public void remove( Object data ) {
if( entryNode != null ) {
Node itr = entryNode;
do {
if( itr.next.data.equals( data ) )
{ //current head(data) in loop equals or data(we gave ) then remove it
if( itr.next == entryNode && entryNode != entryNode.next )
{
// There are still nodes left in the list, but the node
// that we need to remove is the entryNode(first node); so we need
// to reassign the field to the next node in line.
itr.next = itr.next.next;
entryNode = entryNode.next;
} else if( itr.next == itr.next.next ) {
// This condition will only be true if there is only one
// node left in the list, which will be the entryNode.
//
entryNode = null;
} else {
// The node that we need to remove is a regular node,
// i.e. not an entryNode.
//
itr.next = itr.next.next;
}
// Done!
//
return;
}
// Move to the next available node in the list.
//
itr = itr.next;
} while( itr != entryNode );
}
}
/**
* Returns the first occurrence of the node that matches the specified
* data or null if not found. Has a O(n) run-time complexity.
*/
public Node get( Object data ) {
if( entryNode != null ) {
Node itr = entryNode;
do {
if( itr.data.equals( data ) ) {
return itr;
}
itr = itr.next;
} while( itr != entryNode );
}
return null;
}
/**
* Does a full iteration starting and ending at the entry node.
*/
public void iterate( ) {
if( entryNode != null ) {
Node itr = entryNode;
do {
System.out.print( itr.data + " " );
itr = itr.next;
} while( itr != entryNode ); // as circular so 1=last means complete traversals
System.out.println( ); // just for next line..
}
}
/**
* Test Method
*/
public static void main( String[ ] args ) {
// Initialize and populate the circular linked-list
//
CircularLinkedList list = new CircularLinkedList( );
for( int i = 1; i <= 5; i++ ) {
list.add( i );
}
// Prints: 5 4 3 2 1
//
list.iterate( );
// Remove nodes 3, 2, 1 from the circular list.
//
for( int i = 1; i <= 3; i++ ) {
list.remove( list.get( i ).data );
}
// Prints: 5 4
//
list.iterate( );
// Get and remove node 4
//
Node node4 = list.get( 4 );
list.remove( node4.data ); // it can also be done through list.remove(4);
// Prints: 5
//
list.iterate( );
Node node5 = list.get( 5 );
list.remove( node5.data ); list.iterate( );
}
}
Algorithms Tutorials 