我一直在努力工作数小时,试图按字母顺序排列链接列表(类似字典)。给定的字符串只是小写。 例如,输入:“你好,我的名字是伟业”将在列表中进行排序:节点1:阿尔伯特, 节点2:你好, 节点3:是, 等。按字母顺序排列java链接列表(类似字典)
我的代码远远读取像上面的例子一样的字符串,并将其作为节点插入 - 无序。
我在网上搜索的方式来排序链接列表的字母顺序与良好的性能,我发现合并排序可以是有用的。 我已经改变了合并排序为使用的compareTo()字符串的工作,但我的代码返回NullPointerException异常错误以下行:
if(firstList._word.compareTo(secondList._word) < 0){
我寻求帮助来解决下面的代码或另一种方式对于按字母顺序排序链表(不Collection.sort)
我完整的代码(尝试添加的合并排序我的代码工作后):
public class TextList
{
public WordNode _head;
public TextList()
{
_head = null;
}
public TextList (String text)
{
this._head = new WordNode();
int lastIndex = 0;
boolean foundSpace = false;
String newString;
WordNode prev,next;
if (text.length() == 0) {
this._head._word = null;
this._head._next = null;
}
else {
for (int i=0;i<text.length();i++)
{
if (text.charAt(i) == ' ') {
newString = text.substring(lastIndex,i);
insertNode(newString);
// Update indexes
lastIndex = i;
// set to true when the string has a space
foundSpace = true;
}
}
if (!foundSpace) {
//If we didnt find any space, set the given word
_head.setWord(text);
_head.setNext(null);
}
else {
//Insert last word
String lastString = text.substring(lastIndex,text.length());
WordNode lastNode = new WordNode(_head._word,_head._next);
_head.setNext(new WordNode(lastString,lastNode));
}
sortList(_head);
}
}
private void insertNode(String word)
{
//Create a new node and put the curret node in it
WordNode newWord = new WordNode(_head._word,_head.getNext());
//Set the new information in the head
_head._word = word;
_head.setNext(newWord);
}
private WordNode sortList(WordNode start) {
if (start == null || start._next == null) return start;
WordNode fast = start;
WordNode slow = start;
// get in middle of the list :
while (fast._next!= null && fast._next._next !=null){
slow = slow._next; fast = fast._next._next;
}
fast = slow._next;
slow._next=null;
return mergeSortedList(sortList(start),sortList(fast));
}
private WordNode mergeSortedList(WordNode firstList,WordNode secondList){
WordNode returnNode = new WordNode("",null);
WordNode trackingPointer = returnNode;
while(firstList!=null && secondList!=null){
if(firstList._word.compareTo(secondList._word) < 0){
trackingPointer._next = firstList; firstList=firstList._next;
}
else {
trackingPointer._next = secondList; secondList=secondList._next
;}
trackingPointer = trackingPointer._next;
}
if (firstList!=null) trackingPointer._next = firstList;
else if (secondList!=null) trackingPointer._next = secondList;
return returnNode._next;
}
public String toString() {
String result = "";
while(_head.getNext() != null){
_head = _head.getNext();
result += _head._word + ", ";
}
return "List: " + result;
}
public static void main(String[] args) {
TextList str = new TextList("a b c d e a b");
System.out.println(str.toString());
}
}
你确定你不想使用Java提供的实用程序吗? “没有Collection.sort”的 – SMA
。为什么? – Manu
双旋转快速排序的平均排序时间非常快。 –