我必须使用我自己的构造函数实现双循环链表,我已经完成了但是无法弄清楚为什么remove方法不起作用。
我做了大量的研究,但我很难找到符合我需求的任何东西。问题是我没有永久的头尾指针,就像通常在双向链表中一样,但必须使用“标题”作为起点和终点。
带有header元素的构造函数
public MyDoubleLinkedList() {
header = new DEntry(0, null, null);
header.next = header;
header.previous = header;
size = 0;
}
listEntrys的内部类
class DEntry {
/** the data element represented by this entry */
private final int data;
/** reference to the previous element in the list */
private DEntry previous;
/** reference to the next element in the list */
private DEntry next;
/**
* @param data the data object this entry represents
* @param previous reference to the previous element in the list
* @param next reference to the next element in the list
*/
public DEntry(int data, DEntry previous, DEntry next) {
this.data = data;
this.previous = previous;
this.next = next;
}
}
添加到列表的方法:
/**
* Adds a new element into the list at the position specified
*
* @param position the 0 based position at which to add the passed value
* @param value the value to add
* @return 0 if adding was successful, -1 if not
*/
public int add(int position, int value) {
// TODO: please put your code here
DEntry listEntry = new DEntry(value, null, null);
DEntry temp = header;
int i = 0;
if (position < 0 || position > size) {
return -1;
}
if (position == 0) {
temp = header;
} else {
while (i < position) {
temp = temp.next;
i++;
}
}
listEntry.next = temp.next;
listEntry.previous = temp.next;
temp.next = listEntry;
temp.next.previous = listEntry.next;
size++;
return 0;
}
从列表中删除的方法
/**
* Removes an element at the position specified from the list
*
* @param position the 0 based position of the value to remove
* @return value of the removed entry if removing was successful, -1 if not
*/
public int remove(int position) {
// TODO: please put your code here
DEntry toBeDeleted = header;
if(position < 0 || position > size) {
return -1;
}
if(getEntry(position) == null) {
return -1;
} else {
toBeDeleted = getEntry(position);
}
int dataOfDeletedNode = toBeDeleted.data;
if(position == 0) {
header.previous.next = toBeDeleted.next;
header.next.previous = toBeDeleted.previous;
} else if(position == size){
toBeDeleted.previous.next = header.next;
toBeDeleted.next.previous = toBeDeleted.previous;
} else {
toBeDeleted.previous.next = toBeDeleted.next;
toBeDeleted.next.previous = toBeDeleted.previous;
}
size--;
System.out.println(dataOfDeletedNode);
return dataOfDeletedNode;
}
如果我运行代码
list.add(0, 10);
list.add(1, 20);
list.add(0, 30);
remove(1); // 10 should be deleted
而不是30,20,我只有20。
看来你的主要问题来源是add方法。实际上,链接代码中的新节点存在很大问题,这是我通过阅读代码检测到的唯一问题。因此,你的add方法应该是这样的:
public int add(int position, int value) {
DEntry listEntry = new DEntry(value, null, null);
DEntry temp = header;
if (position < 0 || position > size) {
return -1;
}
if (position == 0) {
temp = header;
} else {
int i = 0;
while (i < position) {
temp = temp.next;
i++;
}
}
listEntry.next = temp.next;
listEntry.previous = temp;
temp.next = listEntry;
size++;
return 0;
}
我可以在此期间解决这个问题。确实是我的add方法阻止了我的remove方法正常工作。
部分出现问题的是我的while循环停止了(i
这是我在add方法中提出的,一切都运行正常。
public int add(int position, int value) {
// Creates a new listEntry
DEntry listEntry = new DEntry(value, null, null);
DEntry temp = header;
int i = 0;
if (position < 0 || position > size) {
return -1;
}
while (i <= position) {
temp = temp.next;
i++;
}
// setting the elements neighbours
listEntry.next = temp;
listEntry.previous = temp.previous;
// placing the new element between last and next
temp.previous.next = listEntry;
temp.previous = listEntry;
// places the new entry in the list
temp = listEntry;
size++;
return 0;
}