[英]single linked list to circular linked list
I have been trying to make my single linked list into a doubly-circular one by adjusting my add() and remove() methods. 我一直在尝试通过调整我的add()和remove()方法使单个链接列表变成一个双循环列表。
Here's my code: 这是我的代码:
private LLNode<E> head; // the first node in the list
private LLNode<E> tail; // the last node in the list
// Adds the specified new item to the back of the list.
public void add(E newData)
{
if (head == null) // if the list is empty...
addToHead(newData);
else
addAfter(newData, nodeAt(size - 1));
}
// Removes and returns the item at the specified index of the list.
public E remove(int index)
{
if (index == 0) // if removing from the head...
return removeFromHead();
else
return removeAfter(nodeAt(index - 1));
}
private void addToHead(E newItem)
{
LLNode<E> newNode = new LLNode<E>();
newNode.data = newItem;
newNode.next = head;
head = newNode;
head.prev = tail;
tail.next = newNode;
size++;
}
// Removes the head node from the list.
private E removeFromHead()
{
if (head != null) {
E temp = head.data;
head = head.next;
head.prev = tail;
tail.next = head;
size--;
return temp;
} else
throw new NoSuchElementException();
}
// Adds a new node containing the specified data, after the
// specified node in the list.
private void addAfter(E newItem, LLNode<E> where)
{
if (where != null) {
LLNode<E> newNode = new LLNode<E>();
newNode.data = newItem;
newNode.next = where.next;
where.next = newNode;
newNode.prev = where;
size++;
} else {
throw new NoSuchElementException();
}
}
// Removes the node after the specified node in the list.
private E removeAfter(LLNode<E> where)
{
if (where != null && where.next != null) {
E temp = where.next.data;
where.next = where.next.next;
where.next.prev = where;
size--;
return temp;
} else
throw new NoSuchElementException();
}
In my main method: 在我的主要方法中:
TopSpinLinkedList<Integer> ll = new TopSpinLinkedList<Integer>(numTokens, spinSize);
//fills LinkedList with tokens
for(int i = 1; i <= numTokens; i++) {
ll.add(i);
}
When I try to call this method: 当我尝试调用此方法时:
//shifts all elements in LinkedList to left by one
public void shiftLeft()
{
if(head == null || head.next == null)
return;
LLNode<E> temp = new LLNode<E>();
temp = head;
head = head.next;
temp.next = null;
tail.next = temp;
tail = temp;
}
A NullPointerException appears during runtime. 在运行时出现NullPointerException。 Im pretty sure it has something to do with my add() and remove() methods.
我很确定这与我的add()和remove()方法有关。 I just don't understand what exactly I'm doing wrong to make it into a doubly-circular-linked-list.
我只是不明白我到底在做错什么,使它成为一个双向循环链接列表。 Any help would be very much appreciated.
任何帮助将不胜感激。
In your addToHead
method, are you sure you have initialized your tail
variable when you're doing tail.next = newNode
? 在
addToHead
方法中,确定要在执行tail.next = newNode
时初始化了tail
变量吗?
Try this : 尝试这个 :
private void addToHead(E newItem)
{
LLNode<E> newNode = new LLNode<E>();
newNode.data = newItem;
head = newNode;
tail = newNode;
newNode.prev = newNode.next = newNode;
size++;
}
private void addToHead(E newItem){
LLNode<E> newNode = new LLNode<E>();
newNode.data = newItem;
// head and tail are empty
head = newNode;
tail = newNode;
head.next = newNode;
tail.next = newNode;
head.prev = newNode;
tail.prev = newNode;
}
private void addAfter(E newItem, LLNode<E> where){
if (where != null) {
LLNode<E> newNode = new LLNode<E>();
newNode.data = newItem;
//this part is what you need
newNode.next = where;
newNode.prev = where.prev;
where.prev.next = newNode;
where.prev = newNode;
size++;
} else {
throw new NoSuchElementException();
}
}
//I have changed my code, this should work now. //我已经更改了代码,现在应该可以了。 //I shifted the element
where
one position right and inserted newNode in its position. //我移位元件
where
一个位置向右,并在其位置插入newNode。
Also, if you are using doubly circular linked list, you dont need to have tail. 另外,如果您使用的是双向循环链表,则不需要尾巴。 You can simply get rid of it.
您可以简单地摆脱它。
template<class T> ostream& operator<<(ostream& os, CircularList<T>& ll) { if(!(ll.isEmpty())) { os<<"["; int size=ll.size(); int counting=0; while(counting<size) { os<<ll.get(counting); if(counting+1<size) os<<","; counting++; } os<<"]"; } else { os<<"[]"; } } template<class T> CircularList<T>::CircularList() { this->head = NULL; } template<class T> CircularList<T>::CircularList(const CircularList<T>& other) { this->head=0; Node<T>* tempHead=other.getLeader(); while(tempHead!=0) { Node<T> *temp = new Node<T>(tempHead->data); temp->next = 0; Node<T>* curr = this->getLeader(); if (curr != 0) { while (curr->next != 0) { curr = curr->next; } curr->next = temp; } else { this->head = temp; } tempHead=tempHead->next; } } template<class T> CircularList<T>& CircularList<T>::operator=(const CircularList<T>& other) { if(&other != this) { this->head=0; Node<T>* tempHead=other.head; while(tempHead!=0) { Node<T>* temp = new Node<T>(tempHead->data); temp->next = 0; Node<T>* curr = this->head; if (curr != 0) { while (curr->next != 0) { curr = curr->next; } curr->next = temp; } else { this->head = temp; } tempHead=tempHead->next; } } return *this; } template<class T> CircularList<T>* CircularList<T>::clone() { CircularList<T>* circle = new CircularList<T>(*this); } template<class T> CircularList<T>::~CircularList() { int count =size(); Node<T>* current = this->head; int i=0; while (i<count) { Node<T>* next = current->next; delete current; current = next; i++; } this->head = 0; } template<class T> void CircularList<T>::insert(int index, T data) { Node<T> *j= new Node<T>(data); if((0 <= index) &&( index<= size())) { if(index==0) { if(isEmpty()) { this->head=j; } else { Node<T>*skipping=this->head; this->head=j; this->head->next=skipping; } } else { Node<T> *tempping =this->head; int counting =1; while(counting!=index) { tempping=tempping->next; counting++; } j->next=tempping->next; tempping->next=j; } } else { throw ("invalid index"); } } template<class T> T CircularList<T>::remove(int index) { T pet; if(0 <= index && index<= size()-1) { if(!isEmpty()) { Node<T> *ret=getLeader(); Node<T>* skip=NULL; if(index!=0) { int i=1; while(i!=(index)) { ret=ret->next; i++; } skip=ret; pet=get(index); ret=ret->next; if(ret->next==NULL) { delete ret; skip->next=NULL; ret=NULL; } else { skip->next=ret->next; delete ret; ret=NULL; } } else { Node<T> *tmp = this->head->next; pet=get(index); delete this->head; this->head = tmp; } return pet; } else { throw ("Empty list"); } } else { throw ("Invalid index"); } } template<class T> T CircularList<T>::get(int index) const { if(this->head!=NULL) { if(0 <= index && index<= size()-1) { int counting=0; Node<T>* p =this->head; while(p!=NULL) { if(counting==index) { return p->data; } counting++; p=p->next; } } else { throw ("invalid index"); } } else { throw("empty list"); } } template<class T> bool CircularList<T>::isEmpty() { if(this->head==0) { return true ; } else { return false; } } template<class T> void CircularList<T>::clear() { Node<T>*serp=this->head; while(this->head!=NULL) { this->head=this->head->next; delete serp; serp=this->head; } } template<class T> Node<T>* CircularList<T>::getLeader() const { return this->head; } template<class T> ostream& CircularList<T>::print(ostream& os) { os<<*this; } template<class T> int CircularList<T>::size() const { int counting=0; Node<T> *serp =getLeader(); while(serp!=NULL) { serp=serp->next; counting++; } return counting; } template <class T> CircularList<T>& CircularList<T>::operator+(const CircularList<T>& other) { CircularList<T>* serp=new CircularList<T>(*this); Node<T>* hey=other.getLeader(); int counting=serp->size(); int position=0; while(hey!=NULL) { serp->insert(counting,other.get(position)); hey=hey->next; position++; counting++; } return *serp; } //a friend asked me to help him with some assignment i still have the code
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