Mega Code Archive
Simple linked list class which uses a Comparator to sort the nodes
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//
// Copyright (C) CSIRO Australia Telescope National Facility
//
// This library is free software; you can redistribute it and/or
// modify it under the terms of the GNU Library General Public License
// as published by the Free Software Foundation; either version 2
// of the License, or (at your option) any later version.
//package atnf.atoms.mon.util;
import java.util.Comparator;
import java.util.Vector;
/**
* Simple linked list class which uses a Comparator to sort the nodes. Most
* operations are completed in linear time in the worst case.
*
* @author David Brodrick
*/
public class SortedLinkedList {
/** Trivial class for each list node. */
private class ListNode {
/** The data stored at this node. */
Object data = null;
/** Pointer to the next node. */
ListNode next = null;
ListNode(Object o) {
data = o;
}
ListNode(Object o, ListNode n) {
data = o;
next = n;
}
}
/** Comparator to use. */
protected Comparator itsComparator = null;
/** Head of the list. */
protected ListNode itsHead = null;
/** Tail of the list. */
protected ListNode itsTail = null;
/** Record the current number of nodes in the list. */
protected int itsSize = 0;
/**
* Constructor.
*
* @param c
* The Comparator to use to compare elements.
*/
public SortedLinkedList(Comparator c) {
itsComparator = c;
}
/** Add the Object to the set. */
public synchronized void add(Object o) {
if (o == null) {
return;
}
ListNode newnode = new ListNode(o);
if (itsHead == null) {
// The list was empty
itsHead = itsTail = new ListNode(o);
} else {
// Check if it needs to go right at the head
if (itsComparator.compare(o, itsHead.data) <= 0) {
newnode.next = itsHead;
itsHead = newnode;
}
// Check if it needs to go right at the tail
else if (itsComparator.compare(o, itsTail.data) >= 0) {
itsTail.next = newnode;
itsTail = newnode;
} else {
// It needs to be inserted into the middle of the list
ListNode next = itsHead.next;
ListNode prev = itsHead;
while (itsComparator.compare(o, next.data) > 0) {
prev = next;
next = next.next;
}
// Do the actual insertion
prev.next = newnode;
newnode.next = next;
}
}
itsSize++;
}
/** Remove all instances of the object from the set. */
public synchronized void remove(Object o) {
ListNode next = itsHead;
ListNode prev = null;
while (next != null) {
if (next.data == o) {
// Need to remove this node
itsSize--;
if (prev != null) {
// It's not the head
prev.next = next.next;
} else {
// It was the head
itsHead = next.next;
}
// Check if it's the tail
if (next == itsTail) {
itsTail = prev;
}
}
prev = next;
next = next.next;
}
}
/** Return a reference to the first node but do not remove it */
public synchronized Object first() {
if (itsHead == null) {
return null;
} else {
return itsHead.data;
}
}
/**
* Return all elements less than the argument and remove them from the list.
*/
public synchronized Vector headSet(Object o) {
Vector<Object> res = new Vector<Object>();
// Keep adding the head until it no longer matches
while (itsHead != null && itsComparator.compare(itsHead.data, o) < 0) {
res.add(itsHead.data);
itsSize--;
if (itsHead == itsTail) {
// the list has been emptied
itsHead = itsTail = null;
break;
}
itsHead = itsHead.next;
}
return res;
}
/**
* Check if the list is empty.
*
* @return <code>True</code> if the list is empty.
*/
public synchronized boolean isEmpty() {
if (itsHead == null) {
return true;
}
assert itsSize > 0;
return false;
}
/** Check if the object is already stored in the list. */
public synchronized boolean contains(Object o) {
ListNode next = itsHead;
while (next != null) {
if (next.data == o) {
return true;
}
next = next.next;
}
return false;
}
/** Get a string representation of the list. */
public synchronized String toString() {
String res = "[ ";
ListNode next = itsHead;
while (next != null) {
res = res + next.data.toString() + " ";
next = next.next;
}
res = res + " ]";
return res;
}
/** Return the number of nodes currently in the list. */
public int size() {
return itsSize;
}
}
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