(免责声明:对于学校,因此无法导入其他Java实用程序)
所以我必须在链表上合并排序,而我几乎全部都在关闭。这是:
class musicNode {
String track; // The name of the track
int played= 0; // The number of times played
int shuffleTag= 0; // For shuffling
musicNode next;
public musicNode() { // Here's how we construct an empty list.
next = null;
}
public musicNode(String t) {
track = t; next = null;
}
public musicNode(String t, musicNode ptr) {
track = t; next = ptr;
}
public boolean LTTrack(musicNode x) { // Compares tracks according to alphabetical order on strings
if (this.track.compareTo(x.track)<=0) return true;
else return false;
}
};
// This class represents a playlist;
// We assume that each track appears at most once in the playlist
public class MusicPlayer {
protected musicNode head = null; // Pointer to the top of the list.
int length=0; // the number of nodes in the list.
boolean debug= false;
public MusicPlayer() {
}
public void setToNull() {
head = null;
}
public boolean isEmpty() {
return head == null;
}
public musicNode head() {
return head;
}
void insertTrack(String name) { // Inserts a new track at the top of the list.
musicNode temp= new musicNode(name, head);
head= temp;
length++;
}
void sortTrack() { // TODO
musicNode main = this.head;
mergeSort(main);
}
public musicNode mergeSort(musicNode head) {
if ((head == null) || (head.next == null)){
return head;
}
musicNode left = head;
musicNode right = head.next;
while((right != null) && (right.next != null)){
head = head.next;
right = (right.next).next;
}
right = head.next;
head.next = null;
return merge(mergeSort(left), mergeSort(right));
}
还有这个JUnit测试:
public void testSortMixed() {
MusicPlayer trackList= new MusicPlayer();
trackList.insertTrack("d");
trackList.insertTrack("b");
trackList.insertTrack("e");
trackList.insertTrack("a");
trackList.insertTrack("c");
MusicPlayer trackListTwo= new MusicPlayer();
trackListTwo.insertTrack("e");
trackListTwo.insertTrack("d");
trackListTwo.insertTrack("c");
trackListTwo.insertTrack("b");
trackListTwo.insertTrack("a");
trackList.sortTrack();
musicNode tmp= trackList.head;
musicNode tmp2= trackListTwo.head;
for(int i=0; i< 5; i++){
assertEquals(tmp2.track, tmp.track);
tmp2= tmp2.next;
tmp=tmp.next;
}
}
问题在于它会根据您插入的最后一首曲目进行排序,并且仅从此开始。所以说你从a-f插入字母表,但是你输入的最后一个是“c”,它只会显示“cdef”。但如果最后一个是“a”,那么它按预期工作。
它是如何工作的,当你插入一个轨道时,它会插入到列表的开头,而不是结束,成为头部。我觉得这可能是什么搞乱了,因为我调整并从我的笔记和在线插入底部插入。
我不知道如何解释这一点。另外我知道它根据最后插入的内容进行排序(在上面的JUnit测试中它排序为“cde”,因为我创建了一个主函数并使用它来玩)
任何帮助表示感谢。
答案 0 :(得分:1)
关键点是方法sortTrack中的第二行:
void sortTrack() {
musicNode main = this.head;
this.head = mergeSort(main); // you forgot to set the head of linked list to the merged
}
我在我的笔记本电脑上测试过,现在一切顺利xD