java-实现链表反转-递归和非递归实现


对链表中部分节点进行反转操作，这些节点相隔k个：

0->1->2->3->4->5->6->7->8->9

k=2

8->1->6->3->4->5->2->7->0->9

注意1 3 5 7 9 位置是不变的。

解法：

将链表拆成两部分：

a.0->2->4->6->8

b.1->3->5->7->9

将a部分反转，再将a和b合并

==update end==

Java代码







public class LinkListReversing {

public static void main(String[] args) {
LinkList list=new LinkList();
int[] a={1,2,3,4,5};
for(int each:a){
list.add(each);
}
list.display();
list.reverse();
list.display();
list.reverseRecursive(list.getFirstNode());
list.display();
}

}

class LinkList{

private Node firstNode;
private int length;

public LinkList(){
clear();
}

public void clear(){
firstNode=null;
length=0;
}

public Node getFirstNode(){
return firstNode;
}

public boolean add(int data){
Node node=new Node(data);
if(isEmpty()){
firstNode=node;
}else{
Node lastNode=getNodeAt(length);
lastNode.next=node;
}
length++;
return true;
}

public boolean isEmpty(){
//return length==0;
//use assert to get more details when error occurs
boolean result;
if(length==0){
assert firstNode==null;
result=true;
}else{
assert firstNode!=null;
result=false;
}
return result;
}

public void reverse(){
if(firstNode==null)return;
Node p=firstNode;//use p to traverse every node
Node previous=null;
while(p.next!=null){
Node q=p.next;// save p.next first because the next sentence changes p.next
p.next=previous;
previous=p;
p=q;
}
p.next=previous;
firstNode=p;//should not be ignored
}

//recursive
public Node reverseRecursive(Node p){
if(p==null)return null;
if(p.next==null){
firstNode=p;
return p;
}
Node q=p.next;
//reverse the remaining nodes,except p
//when recursive returns,you can regard the link as a link that has just two elements: p-->q
//so the last reversing is simple: q.next=p;p.next=null;
Node ph=reverseRecursive(q);
q.next=p;
p.next=null;
System.out.print("("+ph.data+")");//ph.data=1,always
return ph;
}

public void display(){
Node node=firstNode;
while(node!=null){
System.out.print(node.data+" ");
node=node.next;
}
System.out.println();
}
private Node getNodeAt(int position){
Node re=firstNode;
if(!isEmpty()&&position>1&&position<=length){
for(int count=1;count<position;count++){
re=re.next;
}
}
return re;
}

//use inner class
private class Node{
private int data;
private Node next;

private Node(int data){
this.data=data;
next=null;
}
}
}