题目
链表操作
（1）单链表就地逆置解题思路
1.创建单链表，需要首先写一个单链表的类。
模仿LinkedList写一个SingleLinkedList类。
/**
* Copyright 2014 TJ SPREADTRUM TEST_AF All Right Reserved
*
* @author: hui.qian Created on 2014年12月29日 下午4:55:41 Description:
* @param <E>
*/
public class SingleLinkedList<E> extends AbstractSequentialList<E> implements
List<E>, Deque<E>, Cloneable, java.io.Serializable {
// 单链表的大小.transient表示该属性不能被序列化.
transient int size = 0;
// 第一个结点
transient SingleNode<E> first;
// 最后一个结点
transient SingleNode<E> last;
static class SingleNode<E> {
E item;
SingleNode<E> next;
SingleNode(E element, SingleNode<E> next) {
this.item = element;
this.next = next;
}
@Override
public String toString() {
return "SingleNode{" +
"item=" + item +
'}';
}
}
public SingleLinkedList() {
}
/**
* 通过集合创建单链表
*/
public SingleLinkedList(Collection<? extends E> c) {
this();
addAll(c);
}
// 向链表中添加元素
public boolean add(E e) {
linkLast(e);
return true;
}
/**
* 将e添加到链表的第一个位置
*/
@Override
public void addFirst(E e) {
// TODO Auto-generated method stub
linkFirst(e);
}
/**
* 将e添加到链表的最后一个位置
*/
@Override
public void addLast(E e) {
// TODO Auto-generated method stub
linkLast(e);
}
/**
* 链接第一个节点
* @param e
*/
private void linkFirst(E e) {
SingleNode<E> f = first;
SingleNode<E> newElement = new SingleNode<E>(e, f);
first = newElement;
if (f == null) {
last = newElement;
}
// 链表的结点个数+1
size++;
// 对链表修改的次数+1
modCount++;
}
@Override
public boolean offerFirst(E e) {
// TODO Auto-generated method stub
return false;
}
@Override
public boolean offerLast(E e) {
// TODO Auto-generated method stub
return false;
}
@Override
public E removeFirst() {
// TODO Auto-generated method stub
return null;
}
@Override
public E removeLast() {
// TODO Auto-generated method stub
return null;
}
@Override
public E pollFirst() {
// TODO Auto-generated method stub
return null;
}
@Override
public E pollLast() {
// TODO Auto-generated method stub
return null;
}
/**
* 得到链表中的第一个元素
*/
@Override
public E getFirst() {
// TODO Auto-generated method stub
SingleNode<E> f = first;
if (f == null)
throw new NoSuchElementException();
return f.item;
}
public SingleNode<E> getFirstNode() {
// TODO Auto-generated method stub
SingleNode<E> f = first;
if (f == null)
throw new NoSuchElementException();
return f;
}
@Override
public E getLast() {
final SingleNode<E> l = last;
if (l == null)
throw new NoSuchElementException();
return l.item;
}
public SingleNode<E> getLastNode() {
final SingleNode<E> l = last;
if (l == null)
throw new NoSuchElementException();
return l;
}
private E unlinkFirst(SingleNode<E> f) {
// assert f == first && f != null;
final E element = f.item;
final SingleNode<E> next = f.next;
f.item = null;
f.next = null; // help GC
first = next;
if (next == null)
last = null;
size--;
modCount++;
return element;
}
@Override
public E peekFirst() {
// TODO Auto-generated method stub
return null;
}
@Override
public E peekLast() {
// TODO Auto-generated method stub
return null;
}
@Override
public boolean removeFirstOccurrence(Object o) {
// TODO Auto-generated method stub
return false;
}
@Override
public boolean removeLastOccurrence(Object o) {
// TODO Auto-generated method stub
return false;
}
@Override
public boolean offer(E e) {
// TODO Auto-generated method stub
return false;
}
@Override
public E remove() {
// TODO Auto-generated method stub
return null;
}
@Override
public E poll() {
// TODO Auto-generated method stub
return null;
}
@Override
public E element() {
// TODO Auto-generated method stub
return getFirst();
}
/**
* 查询第一个元素
*/
@Override
public E peek() {
// TODO Auto-generated method stub
final SingleNode<E> f = first;
return (f == null) ? null : f.item;
}
@Override
public void push(E e) {
// TODO Auto-generated method stub
}
/**
* 获得链表第一个元素,并从链表中移除该结点
*/
@Override
public E pop() {
final SingleNode<E> f = first;
return (f == null) ? null : unlinkFirst(f);
}
@Override
public Iterator<E> descendingIterator() {
// TODO Auto-generated method stub
return null;
}
@Override
public ListIterator<E> listIterator(int index) {
// TODO Auto-generated method stub
return null;
}
/**
* 链表的元素大小
* @return
*/
@Override
public int size() {
// TODO Auto-generated method stub
return size;
}
public boolean addAll(Collection<? extends E> c) {
return addAll(size, c);
}
private boolean isPositionIndex(int index) {
return index >= 0 && index <= size;
}
private String outOfBoundsMsg(int index) {
return "Index: " + index + ", Size: " + size;
}
private void checkPositionIndex(int index) {
if (!isPositionIndex(index))
throw new IndexOutOfBoundsException(outOfBoundsMsg(index));
}
/**
* 根据索引值得到结点
*/
SingleNode<E> node(int index) {
// assert isElementIndex(index);
// >>位运算,size向右移动一位
SingleNode<E> x = first;
for (int i = 0; i < index; i++)
x = x.next;
return x;
}
void linkLast(E e) {
final SingleNode<E> l = last;
final SingleNode<E> newNode = new SingleNode<E>(e, null);
last = newNode;
if (l == null)
first = newNode;
else
l.next = newNode;
size++;
modCount++;
}
public boolean addAll(int index, Collection<? extends E> c) {
checkPositionIndex(index);
Object[] a = c.toArray();
int numNew = a.length;
if (numNew == 0)
return false;
SingleNode<E> pred = null, succ;
if (index == size) {
succ = null;
pred = last;
} else {
succ = node(index);
}
for (Object o : a) {
@SuppressWarnings("unchecked")
E e = (E) o;
SingleNode<E> newNode = new SingleNode<E>(e, null);
if (pred == null) {
} else {
pred.next = newNode;
}
pred = newNode;
}
if (succ == null) {
last = pred;
} else {
pred.next = succ;
}
size += numNew;
modCount++;
return true;
}
@Override
public String toString() {
return "SingleLinkedList{" +
"size=" + size +
", first=" + first +
", last=" + last +
'}';
}
}
测试程序
public class Problem24 {
public static void main(String[] args){
Random random = new Random();
SingleLinkedList<Integer> list = new SingleLinkedList<Integer>();
//初始化单向链表
for(int i=0;i<10;i++){
int value = random.nextInt(10);
list.add(value);
}
//颠倒链表
SingleLinkedList.SingleNode<Integer> firstNode = list.getFirstNode();
SingleLinkedList.SingleNode<Integer> currentNode = firstNode;
SingleLinkedList.SingleNode<Integer> beforeNode = null;
while(currentNode!=null&¤tNode.next!=null){
SingleLinkedList.SingleNode<Integer> nextNode = currentNode.next;
currentNode.next = beforeNode;
beforeNode = currentNode;
currentNode = nextNode;
}
firstNode = list.getFirstNode();
System.out.println("Done!"+list.getLast());
}
}
